drm/i915/gt: Add intel_gt_mcr_multicast_rmw() operation

There are cases where we wish to read from any non-terminated MCR
register instance (or the primary instance in the case of GAM ranges),
clear/set some bits, and then write the value back out to the register
in a multicast manner.  Adding a "multicast RMW" will avoid the need to
open-code this.

v2:
 - Return a u32 to align with the recent change to intel_uncore_rmw.

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/20221014230239.1023689-6-matthew.d.roper@intel.com