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

drm/i915/power: 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.

v2: Keep intel_wakeref.h includes as they are

Reviewed-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://patch.msgid.link/f182bd26d5f9a00e843246d4aac8b25ff7531c51.1764076995.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>