drm/exynos: add has_vtsel flag

The exynos fimd provides video type selection bits from system register
but exynos3 series don't has it, so needs has_vtsel flag and we can
distinguish whether set video type selection bits.

Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>