drm: Make the HPD status updates debug logs more readable

Instead of just printing "status updated from 1 to 2", make those enum
numbers immediately readable.

v2: Also patch output_poll_execute() (Daniel Vetter)
v3: Use drm_get_connector_status_name (Ville Syrjälä)

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org> (for v1)
Signed-off-by: Dave Airlie <airlied@redhat.com>