drm/i915/pps: convert intel_wakeref_t to struct ref_tracker *

drm/i915/pps: convert intel_wakeref_t to struct ref_tracker *

Under the hood, intel_wakeref_t is just struct ref_tracker *. Use the
actual underlying type both for clarity (we *are* using intel_wakeref_t
as a pointer though it doesn't look like one) and to help i915, xe and
display coexistence without custom types.

Reviewed-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://patch.msgid.link/e7afaea1a609485f91669a7d3c5d3fde0e0dbf8b.1764076995.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>