dt-bindings: memory: lpddr2: Add revision-id properties

Add optional revision-id standard LPDDR2 properties which will help to
identify memory chip.
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20211006224659.21434-4-digetx@gmail.comSigned-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>

Documentation/devicetree/bindings/memory-controllers/ddr/jedec,lpddr2.yaml

@@ -24,6 +24,18 @@ properties:
           - enum:
               - jedec,lpddr2-nvm
 
+  revision-id1:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    maximum: 255
+    description: |
+      Revision 1 value of SDRAM chip. Obtained from device datasheet.
+
+  revision-id2:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    maximum: 255
+    description: |
+      Revision 2 value of SDRAM chip. Obtained from device datasheet.
+
   density:
     $ref: /schemas/types.yaml#/definitions/uint32
     description: |
@@ -151,6 +163,8 @@ examples:
         compatible = "elpida,ECB240ABACN", "jedec,lpddr2-s4";
         density = <2048>;
         io-width = <32>;
+        revision-id1 = <1>;
+        revision-id2 = <0>;
 
         tRPab-min-tck = <3>;
         tRCD-min-tck = <3>;