drm/amdgpu/display: fix build when CONFIG_DRM_AMD_DC_DCN is not set

Need to guard some things with CONFIG_DRM_AMD_DC_DCN.

Fixes: 41724ea2 ("drm/amd/display: Add DP 2.0 MST DM Support")
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Dave Airlie <airlied@gmail.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211027223914.1776061-1-alexander.deucher@amd.com

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -10683,9 +10683,9 @@ static int amdgpu_dm_atomic_check(struct drm_device *dev,
 	struct dm_crtc_state *dm_old_crtc_state;
 #if defined(CONFIG_DRM_AMD_DC_DCN)
 	struct dsc_mst_fairness_vars vars[MAX_PIPES];
-#endif
 	struct drm_dp_mst_topology_state *mst_state;
 	struct drm_dp_mst_topology_mgr *mgr;
+#endif
 
 	trace_amdgpu_dm_atomic_check_begin(state);
 

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c

@@ -219,7 +219,7 @@ bool dm_helpers_dp_mst_write_payload_allocation_table(
 	struct drm_dp_mst_topology_mgr *mst_mgr;
 	struct drm_dp_mst_port *mst_port;
 	bool ret;
-	u8 link_coding_cap;
+	u8 link_coding_cap = DP_8b_10b_ENCODING;
 
 	aconnector = (struct amdgpu_dm_connector *)stream->dm_stream_context;
 	/* Accessing the connector state is required for vcpi_slots allocation
@@ -239,7 +239,9 @@ bool dm_helpers_dp_mst_write_payload_allocation_table(
 
 	mst_port = aconnector->port;
 
+#if defined(CONFIG_DRM_AMD_DC_DCN)
 	link_coding_cap = dc_link_dp_mst_decide_link_encoding_format(aconnector->dc_link);
+#endif
 
 	if (enable) {