Add support for the DSS controller on TI's AM625 SoC in the tidss
driver.

The AM625 DSS supports 2 video planes connecting to 2 video ports.
The first plane is a full plane supporting all the features, while the
2nd plane is a "lite" plane without scaling support.

The first video port in AM625 DSS internally provides DPI output to 2
OLDI transmitters. Each OLDI TX outputs 4 differential lanes of video
output and 1 of clock output.

This patch does not automatically enable the OLDI features of AM625 yet.
That support for OLDI will be added subsequently.

The second video port outputs DPI data directly out of the SoC. It has
24 data lines and can support a maximum of RGB888 output bus format.
Signed-off-by: Aradhya Bhatia <a-bhatia1@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/20230616150900.6617-3-a-bhatia1@ti.com