drm/i915: Pimp DPLL ref/unref debugs

drm/i915: Pimp DPLL ref/unref debugs

We currently have a debug message in intel_reference_shared_dpll()
but no counterpart in intel_unreference_shared_dpll(). Add one.

Switch to the [CRTC:...] notation for the pipe name while at it.

v2: Use drm_dbg_kms() instead of drm_dbg() (Jani)

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220922191350.4303-1-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>