drm/i915/bxt: Broxton raises the maximum number of planes to 4

Pipe A and b have 4 planes.

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Antti Koskipää <antti.koskipaa@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
1 file changed