python: Improve access to device_addr_t

This makes two changes:
- Add device_addr_t as a type that the Python property tree access can
  handle
- Add a to_dict() call to device_addr_t (in Python) that will return
  a regular dictionary from a device_addr_t for a more Pythonic access.

host/lib/property_tree_python.cpp

@@ -6,6 +6,7 @@
 
 #include "property_tree_python.hpp"
 #include <uhd/property_tree.hpp>
+#include <uhd/types/device_addr.hpp>
 #include <pybind11/pybind11.h>
 #include <pybind11/stl.h>
 #include <string>
@@ -39,6 +40,7 @@ void export_property_tree(py::module& m)
     export_property<double>(m, "double");
     export_property<std::string>(m, "str");
     export_property<bool>(m, "bool");
+    export_property<uhd::device_addr_t>(m, "device_addr");
 
     py::class_<property_tree>(m, "property_tree")
         .def("subtree", &property_tree::subtree, py::arg("path"))
@@ -56,6 +58,9 @@ void export_property_tree(py::module& m)
         .def("access_bool",
             &property_tree::access<bool>,
             py::return_value_policy::reference)
+        .def("access_device_addr",
+            &property_tree::access<uhd::device_addr_t>,
+            py::return_value_policy::reference)
         // End of types
         ;
 }

host/lib/types/types_python.hpp

@@ -43,7 +43,10 @@ void export_types(py::module& m)
         // Methods
         .def("__str__", &uhd::device_addr_t::to_pp_string)
         .def("to_string", &uhd::device_addr_t::to_string)
-        .def("to_pp_string", &uhd::device_addr_t::to_pp_string);
+        .def("to_pp_string", &uhd::device_addr_t::to_pp_string)
+        .def("to_dict", [](uhd::device_addr_t& self) {
+            return static_cast<std::map<std::string, std::string>>(self);
+        });
     // This will allow functions in Python that take a device_addr to also take
     // a string:
     py::implicitly_convertible<std::string, uhd::device_addr_t>();