drm/i915: Implement async flips for bdw

drm/i915: Implement async flips for bdw

Implement async flip support for BDW. The implementation is
similar to the skl+ code. And just like skl/bxt/glk bdw also
needs the disable w/a, thus we need to plumb the desired state
of the async flip all the way down to i9xx_plane_ctl_crtc().

According to the spec we do need to bump the surface alignment
to 256KiB for this. Async flips require an X-tiled buffer so
we don't have to worry about linear.

Cc: Karthik B S <karthik.b.s@intel.com>
Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210111163711.12913-9-ville.syrjala@linux.intel.com
Reviewed-by: Karthik B S <karthik.b.s@intel.com>