callouts: implement metadata handler

Implement handler of the metadata CALLOUT_DEVICE_PATH. This handler will
convert a device path to an inventory path and call out the latter.

Change-Id: Icbf9c841884ec139f35ea2ac94648e355b421bb2
Signed-off-by: Deepak Kodihalli <dkodihal@in.ibm.com>
4 files changed