arm-autonomy/linux-arm-autonomy: Add explicit dependency on bridge.cfg

xenguest-network depends on CONFIG_BRIDGE_NETFILTER, but the default
value changed to 'n' in Linux 5.6
(http://git.yoctoproject.org/cgit.cgi/linux-yocto/commit/?id=98bda63e20daab95bdc084ce00459a4f622a0505

).
Include bridge.cfg to define CONFIG_BRIDGE_NETFILTER manually for Xen
host builds.

Issue-Id: SCM-2057
Signed-off-by: Peter Hoyes <Peter.Hoyes@arm.com>
Change-Id: Id920d14f87a95214ee722007de923fd27b61afb3
Signed-off-by: Jon Mason <jon.mason@arm.com>