drm/i915/pm: Simplify pm hook documentation

drm/i915/pm: Simplify pm hook documentation

Stop spelling out each variant of the hook ("" vs. "_late" vs.
"_early") and just say eg. "@thaw*" to indicate all of them.
Avoids having to update the docs whenever we start/stop using
one of the variants.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250919185015.14561-2-ville.syrjala@linux.intel.com