drm/vesadrm: Prepare color management for palette-based framebuffers

Distiguish between component-based formats and 'the rest' in vesadrm's
color management. Scanout buffers with component-based format allow
for gamma correction. Palette-based formats (i.e., 'the rest') require
palette setup.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://lore.kernel.org/r/20250714151513.309475-9-tzimmermann@suse.de