drm/tidss: Add support for AM62A7 DSS

drm/tidss: Add support for AM62A7 DSS

Add support for the DSS controller on TI's AM62A7 SoC in the tidss
driver.

This controller has 2 video pipelines that can render 2 video planes on
over a screen, using the overlay managers. The output of the DSS comes
from video port 2 (VP2) in the form of RGB88 DPI signals, while the VP1
is tied off inside the SoC.

Also add and use a new type of VP, DISPC_VP_TIED_OFF, for the tied-off
VP1 of AM62A DSS.

Signed-off-by: Aradhya Bhatia <a-bhatia1@ti.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Link: https://lore.kernel.org/r/20231108171619.978438-3-a-bhatia1@ti.com
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>