drm: exynos: hdmi: add support for platform variants for mixer

This patch adds the support for multiple mixer versions avaialble in
various platform variants. Version is passed as a driver data field
instead of paltform data.

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