dt-bindings: sram: Rename A64 SRAM controller compatible

The SRAM mapping controls on Allwinner SoCs is located in a block called
"System Controls". This block also has registers for identifying the SoC,
reading the state of an external boot-related pin, and on some newer SoCs,
glue layer controls for the EMAC Ethernet controller.

The A64 variant compatible is renamed to "allwinner,a64-system-control"
to reflect this. The old A64 compatible is deprecated. So far we haven't
seen any actual use of it.

Acked-by: Maxime Ripard <[e-mail]>
Signed-off-by: Chen-Yu Tsai <[e-mail]>

Documentation/devicetree/bindings/sram/sunxi-sram.txt

···
 Required properties:
 - compatible : should be:
     - "allwinner,sun4i-a10-sram-controller"
-    - "allwinner,sun50i-a64-sram-controller"
+    - "allwinner,sun50i-a64-sram-controller" (deprecated)
+    - "allwinner,sun50i-a64-system-control"
 - reg : sram controller register offset + length
 
 SRAM nodes