drm/mgag200: Set SCROFF in primary-plane code
The SCROFF bit controls reading the primary plane's scanout buffer
from video memory. Set it from primary-plane code, instead of CRTC
code.
v3:
* only flip SCROFF when enabling/disabling the plane (Jocelyn)
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>
Tested-by: Jocelyn Falempe <jfalempe@redhat.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220728124103.30159-9-tzimmermann@suse.de