synx: adding a macro for invalid synx handle

In use cases where some buffers are passed without a synx handle,
the client needs to define an additional parameter to indicate
whether the h_synx field is valid. This adds to the command size.
Assigning h_synx=SYNX_INVALID_HANDLE can avoid this.

Change-Id: Ibf9dcf9641236ab2ad4c106904f3f17c879486bf
Signed-off-by: Pravin Kumar Ravi <quic_pravinku@quicinc.com>

msm/synx/synx_api.h

@@ -14,6 +14,12 @@
 
 #define SYNX_NO_TIMEOUT        ((u64)-1)
 
+/**
+ * SYNX_INVALID_HANDLE      : client can assign the synx handle variable with this value
+ *                            when it doesn't hold a valid synx handle
+ */
+#define SYNX_INVALID_HANDLE 0
+
 /**
  * enum synx_create_flags - Flags passed during synx_create call
  *