ble_mesh: A specific fix for compile warning in idf4.0

Compared with the latest idf, idf4.0 defines BIT(nr) in
the "esp_bit_defs.h" without the pre-condition "#ifndef BIT",
which will cause compile warning when using mesh. So we
include the header file "soc/soc.h" in "mesh_util.h",
which can bypass the definition of "BIT" in "mesh_util.h"
when compiling.

components/bt/esp_ble_mesh/mesh_common/include/mesh_util.h

@@ -15,6 +15,7 @@
 #define _BLE_MESH_UTIL_H_
 
 #include <stddef.h>
+#include "soc/soc.h"
 #include "mesh_types.h"
 
 #ifdef __cplusplus