drm/tidss: Soft Reset DISPC on startup

Soft reset the display subsystem controller on startup and wait for
the reset to complete. This helps the scenario where display was
already in use by some other core before the linux was booted.

Signed-off-by: Devarsh Thakkar <devarsht@ti.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220314113739.18000-1-devarsht@ti.com