drm/tilcdc: implement palette loading for rev1

Revision 1 of the IP doesn't work if we don't load the palette (even
if it's not used, which is the case for the RGB565 format).

Add a function called from tilcdc_crtc_enable() which performs all
required actions if we're dealing with a rev1 chip.

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