drm/exynos/hdmi: fix PHY configuration sequence

Proper PHY configuration should be as follow:
1. set HDMI clock parents to OSCCLK.
2. reconfigure PHY.
3. set HDMI clock parents to PHY.
4. wait for PLL stabilization.

The patch fixes it and consolidates the code.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>