Implement display w/a #1142. This supposedly fixes some underruns
with FBC+VTd. Bspec says we should use the same programming regardless
of circumstances. Apparently we should flip the magic bits before
turning on any planes so let's put this into the early w/as.

Cc: Lee Shawn C <shawn.c.lee@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200924194810.10293-1-ville.syrjala@linux.intel.comReviewed-by: José Roberto de Souza <jose.souza@intel.com>