dt-bindings: Remove more cases of 'allOf' containing a '$ref'

Another round of 'allOf' removals that came in this cycle.

json-schema versions draft7 and earlier have a weird behavior in that
any keywords combined with a '$ref' are ignored (silently). The correct
form was to put a '$ref' under an 'allOf'. This behavior is now changed
in the 2019-09 json-schema spec and '$ref' can be mixed with other
keywords. The json-schema library doesn't yet support this, but the
tooling now does a fixup for this and either way works.

This has been a constant source of review comments, so let's change this
treewide so everyone copies the simpler syntax.

Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/interrupt-controller/loongson,pch-msi.yaml

@@ -25,19 +25,17 @@ properties:
     description:
       u32 value of the base of parent HyperTransport vector allocated
       to PCH MSI.
-    allOf:
-      - $ref: "/schemas/types.yaml#/definitions/uint32"
-      - minimum: 0
-        maximum: 255
+    $ref: "/schemas/types.yaml#/definitions/uint32"
+    minimum: 0
+    maximum: 255
 
   loongson,msi-num-vecs:
     description:
       u32 value of the number of parent HyperTransport vectors allocated
       to PCH MSI.
-    allOf:
-      - $ref: "/schemas/types.yaml#/definitions/uint32"
-      - minimum: 1
-        maximum: 256
+    $ref: "/schemas/types.yaml#/definitions/uint32"
+    minimum: 1
+    maximum: 256
 
   msi-controller: true