drm/format-helper: Rework RGB888-to-XRGB8888 conversion

drm/format-helper: Rework RGB888-to-XRGB8888 conversion

Update RGB888-to-XRGB8888 conversion to support struct iosys_map
and convert all users. Although these are single-plane color formats,
the new interface supports multi-plane formats for consistency with
drm_fb_blit().

v2:
	* add TODO on vaddr location (Sam)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220808125406.20752-10-tzimmermann@suse.de