drm/exynos: add support for hdmiphy power control for exynos5

This patch adds support for controlling power of hdmi phy for
exynos5 soc. A special bit is provided in exynos5 for directly
switching of PHY while in exynos4, phy power needs to be controlled
through i2c settings. I2C configuration may affect the suspend to
resume and wake-up time requirements hence not added.

Signed-off-by: Rahul Sharma <rahul.sharma@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>