drm/i915: Use stashed away hpd isr bits in intel_digital_port_connected()

Get rid of several platform specific variants of
intel_digital_port_connected() and just use the ISR bits we've
stashed away.

v2: Duplicate stuff to avoid exposing platform specific
    functions across files (Jani)

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200311155422.3043-4-ville.syrjala@linux.intel.com


Reviewed-by: Imre Deak <imre.deak@intel.com>