drm/i915/psr: Add mechanism to notify PSR of DC5/6 enable disable

We need to apply/remove workaround for underrun on idle PSR HW issue
(Wa_16025596647) when DC5/6 is enabled/disabled. This patch implements
mechanism to notify PSR about DC5/6 enable/disable and applies/removes the
workaround using this notification.

Bspec: 74115

Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Link: https://lore.kernel.org/r/20250414100508.1208774-9-jouni.hogander@intel.com