drm/i915: Introduce intel_drrs_type_str()

Add helper to get the drrs type as a string, and use it
in a couple of places. Also pimp the debugfs output a bit
while at it.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220311172428.14685-11-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>