This unifies how the primary plane functions work with how the sprite
functions works, which allows us to reuse them to update primary plane
properties.

v2: Moving setting of plane members in the end to take care of failure cases and
not-visible cases (Matt).
Signed-off-by: Sonika Jindal <sonika.jindal@intel.com>
Acked-by: Matt Roper <matthew.d.roper@intel.com>
[danvet: Add a real commit message.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>