drm/i915/dmc: Add interface to control start of PKG C-state exit

Add interface to control if package C exit starts at the start of the
undelayed vblank. This is needed to implement workaround for underrun on
idle PSR HW issue (Wa_16025596647).

Signed-off-by: Jouni Högander <jouni.hogander@intel.com>
Reviewed-by: Mika Kahola <mika.kahola@intel.com>
Link: https://lore.kernel.org/r/20250414100508.1208774-11-jouni.hogander@intel.com