drm/format-helper: Move drm_fb_build_fourcc_list() to sysfb helpers

Only sysfb drivers use drm_fb_build_fourcc_list(). Move the function
to sysfb helpers and rename it accordingly. Update drivers and tests.

v3:
- update naming in tests
v2:
- select DRM_SYSFB_HELPER (kernel test robot)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: José Expósito <jose.exposito89@gmail.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Acked-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://lore.kernel.org/r/20250616083846.221396-4-tzimmermann@suse.de