db845c: Add rb5 support in db845c-userdebug build target

* Enabled multiple appended DTBs support to allow db845c
boot.img/vendor_boot.img to boot on rb5 as well.

* Introduced a vendor.hw property which will be used to run
device specific services.

* Folded Caleb's HDMI audio routing fix.

Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
Change-Id: I779d01946ae359d5c405d959419e29460083e5df
diff --git a/sepolicy/property_contexts b/sepolicy/property_contexts
index 0d68bd3..9c495ab 100644
--- a/sepolicy/property_contexts
+++ b/sepolicy/property_contexts
@@ -1 +1,2 @@
 vendor.usb.controller  u:object_r:vendor_usb_prop:s0
+vendor.hw  u:object_r:vendor_hw_prop:s0