drm/i915/mcr: Hold forcewake and MCR lock over PPAT setup

drm/i915/mcr: Hold forcewake and MCR lock over PPAT setup

PPAT setup involves a series of multicast writes.  This can be optimized
slightly be acquiring forcewake and the steering lock just once for the
entire sequence.

v2:
 - We should use FW_REG_WRITE instead of FW_REG_READ.  (Bala)

Suggested-by: Balasubramani Vivekanandan <balasubramani.vivekanandan@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Balasubramani Vivekanandan <balasubramani.vivekanandan@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221130155852.19601-1-matthew.d.roper@intel.com