manta: enable kgdb on userdebug and eng builds

Enables kgdb over the serial console on devices with userdebug
and eng builds.

Change-Id: I78c32c59b84a583ab39f27c6af81f225f1fdd804
diff --git a/init.manta.rc b/init.manta.rc
index 2b55e40..e2749bf 100755
--- a/init.manta.rc
+++ b/init.manta.rc
@@ -59,3 +59,8 @@
     class main
     disabled
     oneshot
+
+# on userdebug and eng builds, enable kgdb on the serial console
+on property:ro.debuggable=1
+    write /sys/module/kgdboc/parameters/kgdboc ttyFIQ2
+    write /sys/module/fiq_debugger/parameters/kgdb_enable 1