drm/i915/mtl: Correct implementation of Wa_18018781329

Workaround Wa_18018781329 has applied to several recent Xe_HP-based
platforms.  However there are some extra gotchas to implementing this
properly for MTL that we need to take into account:

 * Due to the separation of media and render/compute into separate GTs,
   this workaround needs to be implemented on each GT, not just the
   primary GT.  Since each class of register only exists on one of the
   two GTs, we should program the appropriate registers on each GT.

 * As with past Xe_HP platforms, the registers on the primary GT (Xe_LPG
   IP) are multicast/replicated registers and should be handled with the
   MCR-aware functions.  However the registers on the media GT (Xe_LPM+
   IP) are regular singleton registers and should _not_ use MCR
   handling.  We need to create separate register definitions for the
   Xe_HP multicast form and the Xe_LPM+ singleton form and use each in
   the appropriate place.

 * Starting with MTL, workarounds documented by the hardware teams are
   technically associated with IP versions/steppings rather than
   top-level platforms.  That means we should take care to check the
   media IP version rather than the graphics IP version when deciding
   whether the workaround is needed on the Xe_LPM+ media GT (in this
   case the workaround applies to both IPs and the stepping bounds are
   identical, but we should still write the code appropriately to set a
   proper precedent for future workaround implementations).

 * It's worth noting that the GSC register and the CCS register are
   defined with the same MMIO offset (0xCF30).  Since the CCS is only
   relevant to the primary GT and the GSC is only relevant to the media
   GT there isn't actually a clash here (the media GT automatically adds
   the additional 0x380000 GSI offset).  However there's currently a
   glitch in the bspec where the CCS register doesn't show up at all and
   the GSC register is listed as existing on both GTs.  That's a known
   documentation problem for several registers with shared GSC/CCS
   offsets; rest assured that the CCS register really does still exist.

Cc: Gustavo Sousa <gustavo.sousa@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Fixes: 41bb543f

 ("drm/i915/mtl: Add initial gt workarounds")
Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230125234159.3015385-2-matthew.d.roper@intel.com