bus: sunxi-rsb: Enable by default for ARM64

Allwinner's A64 SoC uses the "Reduced Serial Bus" to communicate with
its companion PMIC.

Since arm64 does not have separate defconfigs for each platform or
processor family, enable this driver by default for ARM64 as well.
Note that the Kconfig symbol already depends on ARCH_SUNXI.
Signed-off-by: NJagan Teki <jagan@amarulasolutions.com>
[wens@csie.org: Refined commit message]
Signed-off-by: NChen-Yu Tsai <wens@csie.org>

drivers/bus/Kconfig

@@ -132,7 +132,7 @@ config SIMPLE_PM_BUS
 
 config SUNXI_RSB
 	tristate "Allwinner sunXi Reduced Serial Bus Driver"
-	  default MACH_SUN8I || MACH_SUN9I
+	  default MACH_SUN8I || MACH_SUN9I || ARM64
 	  depends on ARCH_SUNXI
 	  select REGMAP
 	  help