init.rc: Add support for new USB accessory configurations

Also moved USB scripts to new file init.usb.rc

Change-Id: I98e099fbd8de3eb3e1e18c9ef69312608033a50c
Signed-off-by: Mike Lockwood <lockwood@google.com>
diff --git a/rootdir/Android.mk b/rootdir/Android.mk
index 1a9e06f..e62c3ea 100644
--- a/rootdir/Android.mk
+++ b/rootdir/Android.mk
@@ -50,6 +50,8 @@
 ALL_PREBUILT += $(file)
 $(INSTALLED_RAMDISK_TARGET): $(file)
 
+# init.usb.rc is handled by build/target/product/core.rc
+
 # Just like /system/etc/init.goldfish.sh, the /init.godlfish.rc is here
 # to allow -user builds to properly run the dex pre-optimization pass in
 # the emulator.