drm/i915/pvc: Read correct RP_STATE_CAP register

The SoC registers, including RP_STATE_CAP, have moved to a new location
in GTTMMADR on Ponte Vecchio.  We need to update the register offset
accordingly.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220505213812.3979301-5-matthew.d.roper@intel.com