ARM: EXYNOS: Add platform driver support for Exynos PMU

This patch modifies Exynos Power Management Unit (PMU) initialization
implementation in following way:

- Added platform driver support for Exynos PMU IP.
- Added platform struct exynos_pmu_data to hold platform specific data.
- For each SoC's PMU support now we can add platform data and statically
  bind PMU configuration and SoC specific initialization function.
- Separate each SoC's PMU initialization function and make it as part of
  platform data.
- It also removes uses of soc_is_exynosXYZ().

Signed-off-by: Pankaj Dubey <pankaj.dubey@samsung.com>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Tested-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>