dt-bindings: display/msm: mdss-common: add memory-region property

Add and document the reserved memory region property in the
mdss-common schema.

For now (sdm845-db845c), it points to a framebuffer memory
region reserved by the bootloader for splash screen.
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/549376/
Link: https://lore.kernel.org/r/20230726132719.2117369-1-amit.pundir@linaro.orgSigned-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

Documentation/devicetree/bindings/display/msm/mdss-common.yaml

@@ -77,6 +77,12 @@ properties:
     items:
       - description: MDSS_CORE reset
 
+  memory-region:
+    maxItems: 1
+    description:
+      Phandle to a node describing a reserved framebuffer memory region.
+      For example, the splash memory region set up by the bootloader.
+
 required:
   - reg
   - reg-names