shill: Generate more ModemManager interface bindings.

No functional changes. Refactors the Makefile to add sysroot XML bindings
through a one line change per interface. Refactors Cellular::Start to outline
the separate tasks more clearly.

BUG=chromium-os:18315
TEST=unit tests

Change-Id: I39359ecfc4b8c0290bf67a6f93732f4be4fbbd59
Reviewed-on: http://gerrit.chromium.org/gerrit/5008
Tested-by: Darin Petkov <petkov@chromium.org>
Reviewed-by: Chris Masone <cmasone@chromium.org>
diff --git a/cellular.h b/cellular.h
index 22236fb..00f1afc 100644
--- a/cellular.h
+++ b/cellular.h
@@ -104,6 +104,9 @@
   std::string GetTypeString();
   std::string GetStateString();
 
+  void EnableModem();
+  void GetModemStatus();
+
   Type type_;
   State state_;