drm/exynos: added vp scaling feature for hdmi

This patch adds vp scaling feature for exynos hdmi. Scaling ratio
between source and destination is used for width and height.
Also meaningless variables to set registers are cleaned.

Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>