arm64: exynos: Select SOC specific drivers

Recently some Exynos drivers were moved from arm/mach-exynos to
drivers/soc. Building the directory depends on SOC_SAMSUNG Kconfig
option so we want it also on ARMv8 platforms, even though none of the
drivers support ARMv8 SoCs yet.
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>

arch/arm64/Kconfig.platforms

@@ -36,6 +36,7 @@ config ARCH_EXYNOS
 	select HAVE_S3C_RTC if RTC_CLASS
 	select PINCTRL
 	select PINCTRL_EXYNOS
+	select SOC_SAMSUNG
 	help
 	  This enables support for ARMv8 based Samsung Exynos SoC family.