serial: 8250_omap: Remove custom deprecated baud setting routine

As comments mentioned this is old (and actually deprecated) interface
to set custom baud rates. This interface has limitations as it only
allows to set a single opaque value called "custom_divisor". If the HW
needs more complex settings (like fractional divisor) it must somehow
encode this. This is horrid interface that is very driver specific
and not flexible. Meanwhile Linux has established way to set free
baud rate settings via BOTHER [1]. With all this being said, remove
deprecated interface for good.

Link: https://stackoverflow.com/questions/12646324/how-can-i-set-a-custom-baud-rate-on-linux [1]
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20260122102349.2395423-2-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: andy-shev

drivers/tty/serial/8250/8250_omap.c

@@ -243,22 +243,6 @@ static void omap_8250_get_divisor(struct uart_port *port, unsigned int baud,
 	unsigned int div_13, div_16;
 	unsigned int abs_d13, abs_d16;
 
-	/*
-	 * Old custom speed handling.
-	 */
-	if (baud == 38400 && (port->flags & UPF_SPD_MASK) == UPF_SPD_CUST) {
-		priv->quot = port->custom_divisor & UART_DIV_MAX;
-		/*
-		 * I assume that nobody is using this. But hey, if somebody
-		 * would like to specify the divisor _and_ the mode then the
-		 * driver is ready and waiting for it.
-		 */
-		if (port->custom_divisor & (1 << 16))
-			priv->mdr1 = UART_OMAP_MDR1_13X_MODE;
-		else
-			priv->mdr1 = UART_OMAP_MDR1_16X_MODE;
-		return;
-	}
 	div_13 = DIV_ROUND_CLOSEST(uartclk, 13 * baud);
 	div_16 = DIV_ROUND_CLOSEST(uartclk, 16 * baud);