build-target-bins: add hw-config to be part of fip

If hw-config dtb blob is found in the output path, package it to the
uefi fip image.

Change-Id: Ifee9fcade02a88b72d6341e271f58e8f3545dcad
Signed-off-by: Harry Moulton <harry.moulton@arm.com>
Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>