drm/xe/xe2: Add missing mocs entry

Add index 4 so WB on both L3 and L4 can be used by userspace.

Bspec: 71582
Link: https://lore.kernel.org/all/7oqovb356dx2hm5muop3xjqr4kv7m5fzjisch3vmsmxm33ygtv@eib4jielia35/
Reviewed-by: Matt Roper <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lucas De Marchi <[e-mail]>
Signed-off-by: Rodrigo Vivi <[e-mail]>

drivers/gpu/drm/xe/xe_mocs.c

···
 	MOCS_ENTRY(2, IG_PAT | XE2_L3_3_UC | L4_0_WB, 0),
 	/* Uncached L3 + L4 */
 	MOCS_ENTRY(3, IG_PAT | XE2_L3_3_UC | L4_3_UC, 0),
+	/* Cached L3 + L4 */
+	MOCS_ENTRY(4, IG_PAT | XE2_L3_0_WB | L4_0_WB, 0),
 };
 
 static unsigned int get_mocs_settings(struct xe_device *xe,