drm/i915: Stash hpd status bits under dev_priv

Instead of constnantly having to figure out which hpd status bit
array to use let's store them under dev_priv.

Should perhaps take this further and stash even more stuff to
make the hpd handling more abstract yet.

v2: Remeber cnp (Imre)
    Add MISSING_CASE() for unknown PCHs (Imre)

Cc: Imre Deak <imre.deak@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200507114808.6150-1-ville.syrjala@linux.intel.comReviewed-by: Imre Deak <imre.deak@intel.com>

drivers/gpu/drm/i915/i915_drv.h

@@ -148,6 +148,8 @@ enum hpd_pin {
 struct i915_hotplug {
 	struct delayed_work hotplug_work;
 
+	const u32 *hpd, *pch_hpd;
+
 	struct {
 		unsigned long last_jiffies;
 		int count;