drm/i915: Enable hpd logic only for ports that are present

drm/i915: Enable hpd logic only for ports that are present

Let's enable the hardware hpd logic only for the ports we
can actually use.

In theory this may save some miniscule amounts of power,
and more importantly it eliminates a lot if platform specific
codepaths since the generic thing can now deal with any
combination of ports being present on each SKU.

v2: Deal with DG1
v3: Deal with DG1 some more

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201028213323.5423-18-ville.syrjala@linux.intel.com
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>