dt-bindings: Add compatible for Mali Valhall (JM)

From the kernel's perspective, (pre-CSF, "Job Manager") Valhall is more
or less compatible with Bifrost, although they differ to userspace. Add
a compatible for Valhall to the existing Bifrost bindings documentation.

As the first SoC with a Valhall GPU receiving mainline support, add a
specific compatible for the MediaTek MT8192, which instantiates a
Mali-G57.

v2: Change compatible to arm,mali-valhall-jm (Daniel Stone).

CC: devicetree@vger.kernel.org
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220525145754.25866-2-alyssa.rosenzweig@collabora.com

Documentation/devicetree/bindings/gpu/arm,mali-bifrost.yaml

@@ -14,7 +14,8 @@ properties:
     pattern: '^gpu@[a-f0-9]+$'
 
   compatible:
-    items:
+    oneOf:
+      - items:
           - enum:
               - amlogic,meson-g12a-mali
               - mediatek,mt8183-mali
@@ -24,6 +25,10 @@ properties:
               - rockchip,px30-mali
               - rockchip,rk3568-mali
           - const: arm,mali-bifrost # Mali Bifrost GPU model/revision is fully discoverable
+      - items:
+          - enum:
+              - mediatek,mt8192-mali
+          - const: arm,mali-valhall-jm # Mali Valhall GPU model/revision is fully discoverable
 
   reg:
     maxItems: 1