drm/i915/psr: Use DC_OFF wake reference to block DC6 on vblank enable

drm/i915/psr: Use DC_OFF wake reference to block DC6 on vblank enable

We are observing following warnings:

*ERROR* power well DC_off state mismatch (refcount 0/enabled 1)

gen9_dc_off_power_well_enabled is considering target state DC_STATE_DISABLE
as DC_OFF power well being enabled. Fix this by using wakeref for the
purpose.

To achieve this we need to modify notification code as well. Currently it
is possible that PSR gets notified vblank enable/disable twice on same
status. This is currently not a problem as it is just triggering call to
intel_display_power_set_target_dc_state with same target state as a
parameter. When using wakeref this becomes a problem due to reference
counting. Fix this storing vbank status on last notification and use that
to ensure there are no more than one notification with same vblank status.

v2: ensure there is no subsequent notifications with same status

Fixes: aa451abcffb5 ("drm/i915/display: Prevent DC6 while vblank is enabled for Panel Replay")
Cc: <stable@vger.kernel.org> # v6.13+
Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Michał Grzelak <michal.grzelak@intel.com>
Link: https://patch.msgid.link/20260520104944.239797-2-jouni.hogander@intel.com
(cherry picked from commit 35485ac56d878192a3829a58cb26503125ec7104)
Signed-off-by: Tvrtko Ursulin <tursulin@ursulin.net>