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/db845c/eth_mac_addr.rc b/db845c/eth_mac_addr.rc
index e710c19..a30c0a5 100644
--- a/db845c/eth_mac_addr.rc
+++ b/db845c/eth_mac_addr.rc
@@ -5,5 +5,5 @@
     disabled
     oneshot
 
-on post-fs-data
+on post-fs-data && property:vendor.hw=db45c
     start eth_mac_addr