drm/i915: Nuke dev_priv->irq_port[]

Instead of looping over ports and hpd_pins, let's loop over
the encoders when doing hotplug processing. And instead of
depending on dev_priv->irq_port[] to tell us whether the
encoder has the ->hpd_pulse() hook or not, we can just
check for that directly. So we can just nuke irq_port[] entirely.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180705164357.28512-5-ville.syrjala@linux.intel.com
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>