drm/tests: Do not use drm_fb_blit() in format-helper tests

drm/tests: Do not use drm_fb_blit() in format-helper tests

[ Upstream commit 5a4856e0e38109ba994f369962f054ecb445c098 ]

Export additional helpers from the format-helper library and open-code
drm_fb_blit() in tests. Prepares for the removal of drm_fb_blit(). Only
sysfb drivers use drm_fb_blit(). The function will soon be removed from
format helpers and be refactored within sysfb helpers.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: José Expósito <jose.exposito89@gmail.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Link: https://lore.kernel.org/r/20250616083846.221396-2-tzimmermann@suse.de
Stable-dep-of: 05663d88fd0b ("drm/tests: Fix drm_test_fb_xrgb8888_to_xrgb2101010() on big-endian")
Signed-off-by: Sasha Levin <sashal@kernel.org>