dt-bindings: mfd: syscon: add compatible string for mstar,msc313-pmsleep

Add a compatible string for the pmsleep register region in the
MStar MSC313 SoC.

Link: https://lore.kernel.org/r/20200729150748.1945589-2-daniel@0x0f.comSigned-off-by: Daniel Palmer <daniel@0x0f.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Documentation/devicetree/bindings/mfd/syscon.yaml

@@ -39,6 +39,7 @@ properties:
               - allwinner,sun8i-v3s-system-controller
               - allwinner,sun50i-a64-system-controller
               - microchip,sparx5-cpu-syscon
+              - mstar,msc313-pmsleep
 
           - const: syscon