layer.conf: Add uart0 overlay
layer.conf: Add uart0 overlay

We add the uart0 overlay to the rootfs alongside the
existing uart1 overlay.

Changelog-entry: Add the uart0 overlay to rootfs
Signed-off-by: Florin Sarbu <3a837a37a2ac9072a088641ec330e0e5d5b86f4e@balena.io>

resin-os/resin-raspberrypi,resin-os/resin-raspberrypi