drm/mgag200: Pin displayed cursor BO to video memory

drm/mgag200: Pin displayed cursor BO to video memory

BugLink: https://bugs.launchpad.net/bugs/1851340
The cursor BO has to be pinned to video ram while it's being displayed.
With the current code, the BO might be pinned to system memory instead.
The patch fixes this problem.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Fixes: 94dc57b10399 ("drm/mgag200: Rewrite cursor handling")
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190723075425.24028-2-tzimmermann@suse.de
(cherry picked from commit a0fd72d2c95b56c78feec0867f2077b5ff5991e6)
Signed-off-by: Po-Hsu Lin <po-hsu.lin@canonical.com>
Acked-by: Khalid Elmously <khalid.elmously@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>