drm/i915: Polish the chv cmnlane resrt macros

Replace the semi-funky cmnlane assert/deassert macros with something a
bit more conventional. Also protect the macro arguments properly (also
for  PHY_POWERGOOD()).

Reviewed-by: Rafael Barbalho <rafael.barbalho@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>