dt-bindings: gpu: mali-midgard: Tidy up conversion to YAML

Instead of grouping alphabetically by third-party vendor, leading to
one-element enums, start sorting by Mali model number, as done for
Utgard.

This already allows us to de-duplicate two "arm,mali-t760" sections and
will make it easier to add new vendor compatibles.

Fixes: 553cedf60056 ("dt-bindings: Convert Arm Mali Midgard GPU to DT schema")
Fixes: 1be5b54d26ae ("dt-bindings: gpu: mali-midgard: Add samsung exynos5250 compatible")
Cc: Rob Herring <[e-mail]>
Signed-off-by: Andreas Färber <[e-mail]>
[robh: don't resort everything to avoid conflicts]
Signed-off-by: Rob Herring <[e-mail]>

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

···
     oneOf:
       - items:
           - enum:
+             - samsung,exynos5250-mali
+          - const: arm,mali-t604
+      - items:
+          - enum:
              - allwinner,sun50i-h6-mali
           - const: arm,mali-t720
       - items:
···
       - items:
           - enum:
              - rockchip,rk3288-mali
+             - samsung,exynos5433-mali
           - const: arm,mali-t760
       - items:
           - enum:
              - rockchip,rk3399-mali
           - const: arm,mali-t860
-      - items:
-          - enum:
-             - samsung,exynos5250-mali
-          - const: arm,mali-t604
-      - items:
-          - enum:
-             - samsung,exynos5433-mali
-          - const: arm,mali-t760
 
           # "arm,mali-t624"
           # "arm,mali-t628"