drm/nouveau/kms/nv50-: init hpd_irq_lock for PIOR DP

Fixes OOPS on boards with ANX9805 DP encoders.

Cc: stable@vger.kernel.org # 6.4+
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230719044051.6975-3-skeggsb@gmail.com