dt-bindings: sram: Merge Socionext SRAM bindings into generic

The Socionext SRAM bindings list only compatible so integrate them into
generic SRAM bindings schema.
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/sram/milbeaut-smp-sram.txt

-Milbeaut SRAM for smp bringup
-
-Milbeaut SoCs use a part of the sram for the bringup of the secondary cores.
-Once they get powered up in the bootloader, they stay at the specific part
-of the sram.
-Therefore the part needs to be added as the sub-node of mmio-sram.
-
-Required sub-node properties:
-- compatible : should be "socionext,milbeaut-smp-sram"
-
-Example:
-
-        sram: sram@0 {
-                compatible = "mmio-sram";
-                reg = <0x0 0x10000>;
-                #address-cells = <1>;
-                #size-cells = <1>;
-                ranges = <0 0x0 0x10000>;
-
-                smp-sram@f100 {
-                        compatible = "socionext,milbeaut-smp-sram";
-                        reg = <0xf100 0x20>;
-                };
-        };

Documentation/devicetree/bindings/sram/sram.yaml

@@ -72,6 +72,7 @@ patternProperties:
           - rockchip,rk3066-smp-sram
           - samsung,exynos4210-sysram
           - samsung,exynos4210-sysram-ns
+          - socionext,milbeaut-smp-sram
 
       reg:
         description:
@@ -240,3 +241,17 @@ examples:
             reg = <0x1000 0x8>;
         };
     };
+
+  - |
+    sram@0 {
+        compatible = "mmio-sram";
+        reg = <0x0 0x10000>;
+        #address-cells = <1>;
+        #size-cells = <1>;
+        ranges = <0 0x0 0x10000>;
+
+        smp-sram@f100 {
+            compatible = "socionext,milbeaut-smp-sram";
+            reg = <0xf100 0x20>;
+        };
+    };