disp: msm: dp: compile MST feature based on display config

Add a compile time flag for the MST feature that will allow
selectively enabling the feature.

Change-Id: I8bf288277c7af00c3cf254a8c757151559e0a010
Signed-off-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>

msm/dp/dp_drm.c

@@ -11,6 +11,7 @@
 #include "msm_kms.h"
 #include "sde_connector.h"
 #include "dp_drm.h"
+#include "dp_mst_drm.h"
 #include "dp_debug.h"
 
 #define DP_MST_DEBUG(fmt, ...) DP_DEBUG(fmt, ##__VA_ARGS__)