drm/i915/xehp: GAM registers don't need to be re-applied on engine resets

Register reset characteristics (i.e., whether the register maintains or
loses its value on engine reset) is an important factor that determines
which wa_list we want to add workarounds to.  We recently found out that
the bspec documentation for the Xe_HP's "GAM" registers in the 0xC800 -
0xCFFF range was misleading; these registers do not actually lose their
value on engine resets as the documentation implied.  This means there's
no need to re-apply workarounds touching these registers after a reset,
and the corresponding workarounds should be moved from the 'engine'
lists back to the 'gt' list.

v2:
 - Don't add Wa_18018781329 to xehpsdv; the original condition didn't
   include that platform.  (Gustavo)
 - Move the MTL code to the GT function as-is for now; we'll take care
   of the additional fixes needed in a follow-up patch.

Cc: Gustavo Sousa <gustavo.sousa@intel.com>
Fixes: edf176f4 ("drm/i915/dg2: Move misplaced 'ctx' & 'gt' wa's to engine wa list")
Fixes: b2006061 ("drm/i915/xehpsdv: Move render/compute engine reset domains related workarounds")
Fixes: 41bb543f

 ("drm/i915/mtl: Add initial gt workarounds")
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230125234159.3015385-1-matthew.d.roper@intel.com