drm/bridge: samsung-dsim: allow configuring the MAIN_VSA offset

drm/bridge: samsung-dsim: allow configuring the MAIN_VSA offset

The MAIN_VSA offset of DSIM_MSYNC is hardcoded to a 22-bit offset, but
Exynos7870's DSIM has it in a 16-bit offset as per the downstream kernel
sources.

In order to support both, move this offset value to the driver data
struct and define it for every driver compatible. Reference the value
from there instead, in functions wherever required.

Signed-off-by: Kaustabh Chakraborty <kauschluss@disroot.org>
Signed-off-by: Inki Dae <inki.dae@samsung.com>