ARM: EXYNOS: Move pm_domains driver to drivers/soc/samsung

Exynos PM domains driver does not have mach-specific dependencies so it
can be safely moved out of arm/mach-exynos to drivers/soc. This in
future will allow re-using it on ARM64 boards.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>