arm64: rockchip: Force CONFIG_PM on Rockchip systems

A number of the Rockchip-specific drivers (IOMMU, display controllers)
are now assuming that CONFIG_PM is set, and may completely misbehave
if that's not the case.

Since there is hardly any reason for this configuration option not
to be selected anyway, let's require it (in the same way Tegra already
does).
Signed-off-by: NMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: NOlof Johansson <olof@lixom.net>

arch/arm64/Kconfig.platforms

@@ -151,6 +151,7 @@ config ARCH_ROCKCHIP
 	select GPIOLIB
 	select PINCTRL
 	select PINCTRL_ROCKCHIP
+	select PM
 	select ROCKCHIP_TIMER
 	help
 	  This enables support for the ARMv8 based Rockchip chipsets,