dt-bindings: clk: versaclock5: Add optional load capacitance property

There are two registers which can set the load capacitance for
XTAL1 and XTAL2. These are optional registers when using an
external crystal.  Since XTAL1 and XTAL2 will set to the same value,
update the binding to support a single property called
xtal-load-femtofarads.

Signed-off-by: Adam Ford <aford173@gmail.com>
Link: https://lore.kernel.org/r/20210207185140.3653350-1-aford173@gmail.com
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

Author: aford173

Documentation/devicetree/bindings/clock/idt,versaclock5.yaml

@@ -59,6 +59,12 @@ properties:
     minItems: 1
     maxItems: 2
 
+  idt,xtal-load-femtofarads:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    minimum: 9000
+    maximum: 22760
+    description: Optional load capacitor for XTAL1 and XTAL2
+
 patternProperties:
   "^OUT[1-4]$":
     type: object