drm/i915/xe2lpd: Add DC state support

Xe2_LPD supports DC5, DC6, and DC9 (DC3CO no longer exists).  The
overall programming and requirements to enter DC states are similar to
those of Xe_LPD+ although AUX transactions do not require DC5/DC6 exit
as they did previously.

Bspec: 68851, 68857, 68886, 69115
Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230919192128.2045154-21-lucas.demarchi@intel.com