drm/tidss: remove AM65x PG1 YUV erratum code

AM65x PG1 has a HW issue with YUV pixel formats, resulting in wrong
colors on the screen. This issue is fixed in PG2 hardware.

The driver currently has code to hide YUV pixel formats from the
userspace. To support PG2, we would need to add code to detect the SoC
version and hide the YUV formats based on that.

However, as PG1 will be phased out and PG2 will be the main platform, a
much simpler solution is just to drop the code in question. The downside
is that the users will be able to use YUV formats on PG1, getting wrong
colors on the screen. On the other hand, that may also be a plus, as the
same applications will now work on PG1 and PG2, even if the colors are
wrong on PG1.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200429121022.3871-1-tomi.valkeinen@ti.com
Reviewed-by: Jyri Sarha <jsarha@ti.com>