drm/amd/display: Add customizable tracing event

[why]
add customizable log with a message input, which is for adding
test log in debugging as printf function in ETW.

[Usage]
EVENT_LOG_CUST_MSG1("TestLog","Hello World %d=0x%x", 123, pDC);
Signed-off-by: Chiawen Huang <chiawen.huang@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@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/dm_event_log.h

@@ -33,6 +33,7 @@
 
 #define EVENT_LOG_AUX_REQ(ddc, type, action, address, len, data)
 #define EVENT_LOG_AUX_REP(ddc, type, replyStatus, len, data)
+#define EVENT_LOG_CUST_MSG(tag, a, ...)
 
 #endif