drm/amd/display: allocate 4 ddc engines for RV2

[Why]
Driver will create 0, 1, and 2 ddc engines for RV2,
but some platforms used 0, 1, and 3.

[How]
Still allocate 4 ddc engines for RV2.

Signed-off-by: Derek Lai <Derek.Lai@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@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/dcn10/dcn10_resource.c

@@ -508,7 +508,7 @@ static const struct resource_caps rv2_res_cap = {
 		.num_audio = 3,
 		.num_stream_encoder = 3,
 		.num_pll = 3,
-		.num_ddc = 3,
+		.num_ddc = 4,
 };
 
 static const struct dc_plane_cap plane_cap = {