add function for device-specific wipe data features

Some devices want to do special things when recovery wipes data (eg,
wipe data in their baseband processor as well).  Add a hook in the
device-specific recovery library that gets called when data is wiped.

Also add an amend root for the "mbm" partition.
diff --git a/recovery_ui.h b/recovery_ui.h
index 86f540b..671fe40 100644
--- a/recovery_ui.h
+++ b/recovery_ui.h
@@ -48,6 +48,14 @@
 // information to the screen.
 extern int device_perform_action(int which);
+// Called when we do a wipe data/factory reset operation (either via a
+// reboot from the main system with the --wipe_data flag, or when the
+// user boots into recovery manually and selects the option from the
+// menu.)  Can perform whatever device-specific wiping actions are
+// needed.  Return 0 on success.  The userdata and cache partitions
+// are erased after this returns (whether it returns success or not).
+int device_wipe_data();
 #define NO_ACTION           -1
 #define HIGHLIGHT_UP        -2