drm/i915/gt: Add MCR-specific workaround initializers

Let's be more explicit about which of our workarounds are updating MCR
registers.
Signed-off-by: NMatt Roper <matthew.d.roper@intel.com>
Reviewed-by: NBalasubramani Vivekanandan <balasubramani.vivekanandan@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221014230239.1023689-12-matthew.d.roper@intel.com

drivers/gpu/drm/i915/gt/intel_workarounds_types.h

@@ -15,7 +15,9 @@ struct i915_wa {
 	u32		clr;
 	u32		set;
 	u32		read;
-	bool		masked_reg;
+
+	u32		masked_reg:1;
+	u32		is_mcr:1;
 };
 
 struct i915_wa_list {