drm/komeda: add NV12 format to support writeback layer type

When testing the d71 writeback layer function,
the output format is set to NV12, and the following error message is displayed:

[drm:komeda_fb_is_layer_supported] Layer TYPE: 4 doesn't support fb FMT: NV12 little-endian (0x3231564e) with modifier: 0x0..

Check the d71 data manual, writeback layer output formats includes NV12 format.

Signed-off-by: baozhu.liu <lucas.liu@siengine.com>
Signed-off-by: Liviu Dudau <liviu.dudau@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230829093004.22860-1-lucas.liu@siengine.com