drm/tilcdc: Enable palette loading for revision 2 LCDC too

The LCDC revision 2 documentation also mentions the mandatory palette
for true color modes. Even if the rev 2 LCDC appears to work just fine
without the palette being loaded loading it helps in testing the
feature.

Signed-off-by: Jyri Sarha <jsarha@ti.com>
Tested-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>