drm/i915/pvc: Add forcewake support

Add PVC's forcewake ranges.

v2:
 - Drop replicated comment completely; move general cleanup of the
   documentation to a separate patch.

Bspec: 67609
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Stuart Summers <stuart.summers@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Matt Atwood <matthew.s.atwood@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220511060228.1179450-3-matthew.d.roper@intel.com