drm/ast: cursor: Add support for ARGB4444

Add support for cursor image data in ARGB4444 format. This is the
hardware's native format and requires no conversion.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250217122336.230067-4-tzimmermann@suse.de