drm/i915/dg2: Add support for DC5 state

With the latest DMC in place, enabling DC5 on DG2.

Cc: Imre Deak <imre.deak@intel.com>
Signed-off-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220728183641.55692-1-anusha.srivatsa@intel.com