upm.i: add top level interface file which includes std_string.i

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

src/servo/jsupm_servo.i

@@ -1,4 +1,5 @@
 %module jsupm_servo
+%include "../upm.i"
 
 %{
     #include "servo.h"

src/servo/pyupm_servo.i

@@ -1,4 +1,5 @@
 %module pyupm_servo
+%include "../upm.i"
 
 %feature("autodoc", "3");