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

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

src/hmc5883l/jsupm_hmc5883l.i

@@ -1,4 +1,5 @@
 %module jsupm_hmc5883l
+%include "../upm.i"
 
 %{
     #include "hmc5883l.h"

src/hmc5883l/pyupm_hmc5883l.i

@@ -1,4 +1,5 @@
 %module pyupm_hmc5883l
+%include "../upm.i"
 
 %feature("autodoc", "3");