drm/i915: add port parameter to intel_hdmi_init

Instead of having a giant if cascade to figure this out according to
the passed-in register. We could do quite a bit more cleaning up and
all by using the port at more places, but I think this should be part
of a bigger rework to introduce a struct intel_digital_port which
would keep track of all these things. I guess this will be part of
some haswell-DP-induced refactoring.

For now this rips out the big cascade, which is what annoyed me so
much.

v2: Add port variable name back for the func decl (I've tried to trick
myself below the 80 char limit).

Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>