drm/i915: Use GEN12_RPSTAT register for GT freq

On GEN12+ use GEN12_RPSTAT register to get actual resolved GT
freq. GEN12_RPSTAT does not require a forcewake and will return 0 freq if
GT is in RC6.

v2:
  - Fixed review comments(Ashutosh)
  - Added function intel_rps_read_rpstat_fw to read RPSTAT without
    forcewake, required especially for GEN6_RPSTAT1 (Ashutosh, Tvrtko)
v3:
  - Updated commit title and message for more clarity (Ashutosh)
  - Replaced intel_rps_read_rpstat with direct read to GEN12_RPSTAT1 in
    read_cagf (Ashutosh)
v4: Remove GEN12_CAGF_SHIFT and use REG_FIELD_GET (Rodrigo)

Cc: Don Hiatt <donhiatt@gmail.com>
Cc: Andi Shyti <andi.shyti@intel.com>
Signed-off-by: Don Hiatt <don.hiatt@intel.com>
Signed-off-by: Badal Nilawar <badal.nilawar@intel.com>
Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221114123348.3474216-3-badal.nilawar@intel.com