dt-bindings: mmc: mmc-slot: Make compatible property optional

The compatible property is required for some vendor-specific device trees,
such as Amlogic's meson-mx-sdio, but is unnecessary for others, like
Microchip's DTS. To resolve unintended warnings for configurations that do
not require it, remove compatible from the required properties in
mmc-slot.yaml.

Since meson-mx-sdio still requires compatible, explicitly add it to its
required list in amlogic,meson-mx-sdio.yaml.

Signed-off-by: Dharma Balasubiramani <[e-mail]>
Reviewed-by: Rob Herring (Arm) <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Ulf Hansson <[e-mail]>

Documentation/devicetree/bindings/mmc/amlogic,meson-mx-sdio.yaml

···
       bus-width:
         enum: [1, 4]
 
+    required:
+      - compatible
+
     unevaluatedProperties: false
 
 required:

Documentation/devicetree/bindings/mmc/mmc-slot.yaml

···
     maxItems: 1
 
 required:
-  - compatible
   - reg
 
 unevaluatedProperties: false