drm/amd/display: fix dml handling of mono8/16 pixel formats

mono formats are treated exactly the same as equivallent bpp
444 formats. Dml validation however lacks 444 8 bit format
while dml perf param calculation lacks mono format support

This change makes them equivallent as far as the enum is concerned
to avoid having to update dml

Signed-off-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dml/display_mode_enums.h

@@ -40,8 +40,8 @@ enum source_format_class {
 	dm_422_8 = 5,
 	dm_422_10 = 6,
 	dm_444_8 = 7,
-	dm_mono_8,
-	dm_mono_16
+	dm_mono_8 = dm_444_8,
+	dm_mono_16 = dm_444_16
 };
 enum output_bpc_class {
 	dm_out_6 = 0, dm_out_8 = 1, dm_out_10 = 2, dm_out_12 = 3, dm_out_16 = 4