With this we can treat the fb format modifier completely independently
from the fencing mode in obj->tiling_mode in the initial plane code.
Which means new tiling modes without any gtt fence are now fully
support in the core i915 driver code.

v2: Also add pixel_format while at it, we need this to compute the
height for the new tiling formats.
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>