ARM: EXYNOS: Remove calls to of_genpd_get_from_provider()

Update the EXYNOS PM domain code to use the of_genpd_add_subdomain()
and remove any calls to of_genpd_get_from_provider().

Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>