drm/i915: Convert DIP port switch cases to a simple macro

We have a couple of switch cases to compute the port value for the
VIDEO_DIP_CTL register. Replace them with a simple macro.

We do lose a few BUG() calls, but many people may consider that
an improvement.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --cc drivers/gpu/drm/i915/i915_reg.h
Simple merge

diff --cc drivers/gpu/drm/i915/intel_hdmi.c
Simple merge