drm/i915/uncore: Add GSI offset to uncore

drm/i915/uncore: Add GSI offset to uncore

GT non-engine registers (referred to as "GSI" registers by the spec)
have the same relative offsets on standalone media as they do on the
primary GT, just with an additional "GSI offset" added to their MMIO
address.  If we store this GSI offset in the standalone media's
intel_uncore structure, it can be automatically applied to all GSI reg
reads/writes that happen on that GT, allowing us to re-use our existing
GT code with minimal changes.

Forcewake and shadowed register tables for the media GT (which will be
added in a future patch) are listed as final addresses that already
include the GSI offset, so we also need to add the GSI offset before
doing lookups of registers in one of those tables.

v2:
 - Add comment on raw_reg_*() macros explaining why we don't bother with
   GSI offsets in them.  (Daniele)

Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220908224550.821257-1-matthew.d.roper@intel.com
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>