drm/bridge: samsung-dsim: support separate LINK and DPHY status registers

drm/bridge: samsung-dsim: support separate LINK and DPHY status registers

Exynos7870's DSIM has separate registers for LINK and DPHY status. This
is in contrast to older variants in the driver which use a single
register for both.

Add a driver data flag which indicates that the device variant supports
the legacy status register. Change the register read calls
appropriately.

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