ARM: dts: microchip: sam9x60: Add missing property atmel,usart-mode

Add the atmel,usart-mode property to the UART nodes. This ensures
compliance with the atmel,at91-usart.yaml schema and resolves the errors
below:
serial@200: $nodename:0: 'serial@200' does not match
'^spi(@.*|-([0-9]|[1-9][0-9]+))?$'
serial@200: atmel,use-dma-rx: False schema does not allow True
serial@200: atmel,use-dma-tx: False schema does not allow True
serial@200: atmel,fifo-size: False schema does not allow [[16]]

These errors indicate that the property
atmel,usart-mode = <AT91_USART_MODE_SERIAL> is missing for
UART nodes 0, 1, 2, 3, 4, 6, 7, 8, 9, 10, 11, and 12.

Fixes: 99c8083 ("ARM: dts: at91: sam9x60: Add missing flexcom definitions")
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Andrei Simion <andrei.simion@microchip.com>
Link: https://lore.kernel.org/r/20240912093307.40488-1-andrei.simion@microchip.com
[claudiu.beznea: move the atmel,usart-mode close to vendor specific
 properties to cope with DTS coding style]
Signed-off-by: Claudiu Beznea <claudiu.beznea@tuxon.dev>

Author: Andrei Simion

arch/arm/boot/dts/microchip/sam9x60.dtsi

@@ -186,6 +186,7 @@
 					dma-names = "tx", "rx";
 					clocks = <&pmc PMC_TYPE_PERIPHERAL 13>;
 					clock-names = "usart";
+					atmel,usart-mode = <AT91_USART_MODE_SERIAL>;
 					atmel,use-dma-rx;
 					atmel,use-dma-tx;
 					atmel,fifo-size = <16>;
@@ -388,6 +389,7 @@
 					dma-names = "tx", "rx";
 					clocks = <&pmc PMC_TYPE_PERIPHERAL 32>;
 					clock-names = "usart";
+					atmel,usart-mode = <AT91_USART_MODE_SERIAL>;
 					atmel,use-dma-rx;
 					atmel,use-dma-tx;
 					atmel,fifo-size = <16>;
@@ -439,6 +441,7 @@
 					dma-names = "tx", "rx";
 					clocks = <&pmc PMC_TYPE_PERIPHERAL 33>;
 					clock-names = "usart";
+					atmel,usart-mode = <AT91_USART_MODE_SERIAL>;
 					atmel,use-dma-rx;
 					atmel,use-dma-tx;
 					atmel,fifo-size = <16>;
@@ -598,6 +601,7 @@
 					dma-names = "tx", "rx";
 					clocks = <&pmc PMC_TYPE_PERIPHERAL 9>;
 					clock-names = "usart";
+					atmel,usart-mode = <AT91_USART_MODE_SERIAL>;
 					atmel,use-dma-rx;
 					atmel,use-dma-tx;
 					atmel,fifo-size = <16>;
@@ -649,6 +653,7 @@
 					dma-names = "tx", "rx";
 					clocks = <&pmc PMC_TYPE_PERIPHERAL 10>;
 					clock-names = "usart";
+					atmel,usart-mode = <AT91_USART_MODE_SERIAL>;
 					atmel,use-dma-rx;
 					atmel,use-dma-tx;
 					atmel,fifo-size = <16>;
@@ -700,6 +705,7 @@
 					dma-names = "tx", "rx";
 					clocks = <&pmc PMC_TYPE_PERIPHERAL 11>;
 					clock-names = "usart";
+					atmel,usart-mode = <AT91_USART_MODE_SERIAL>;
 					atmel,use-dma-rx;
 					atmel,use-dma-tx;
 					atmel,fifo-size = <16>;
@@ -751,6 +757,7 @@
 					dma-names = "tx", "rx";
 					clocks = <&pmc PMC_TYPE_PERIPHERAL 5>;
 					clock-names = "usart";
+					atmel,usart-mode = <AT91_USART_MODE_SERIAL>;
 					atmel,use-dma-rx;
 					atmel,use-dma-tx;
 					atmel,fifo-size = <16>;
@@ -821,6 +828,7 @@
 					dma-names = "tx", "rx";
 					clocks = <&pmc PMC_TYPE_PERIPHERAL 6>;
 					clock-names = "usart";
+					atmel,usart-mode = <AT91_USART_MODE_SERIAL>;
 					atmel,use-dma-rx;
 					atmel,use-dma-tx;
 					atmel,fifo-size = <16>;
@@ -891,6 +899,7 @@
 					dma-names = "tx", "rx";
 					clocks = <&pmc PMC_TYPE_PERIPHERAL 7>;
 					clock-names = "usart";
+					atmel,usart-mode = <AT91_USART_MODE_SERIAL>;
 					atmel,use-dma-rx;
 					atmel,use-dma-tx;
 					atmel,fifo-size = <16>;
@@ -961,6 +970,7 @@
 					dma-names = "tx", "rx";
 					clocks = <&pmc PMC_TYPE_PERIPHERAL 8>;
 					clock-names = "usart";
+					atmel,usart-mode = <AT91_USART_MODE_SERIAL>;
 					atmel,use-dma-rx;
 					atmel,use-dma-tx;
 					atmel,fifo-size = <16>;
@@ -1086,6 +1096,7 @@
 					dma-names = "tx", "rx";
 					clocks = <&pmc PMC_TYPE_PERIPHERAL 15>;
 					clock-names = "usart";
+					atmel,usart-mode = <AT91_USART_MODE_SERIAL>;
 					atmel,use-dma-rx;
 					atmel,use-dma-tx;
 					atmel,fifo-size = <16>;
@@ -1137,6 +1148,7 @@
 					dma-names = "tx", "rx";
 					clocks = <&pmc PMC_TYPE_PERIPHERAL 16>;
 					clock-names = "usart";
+					atmel,usart-mode = <AT91_USART_MODE_SERIAL>;
 					atmel,use-dma-rx;
 					atmel,use-dma-tx;
 					atmel,fifo-size = <16>;