dtoverlay: Create "/aliases" node when needed
dtoverlay: Create "/aliases" node when needed

Attempting to add an alias currently fails if there is no
existing "/aliases" node. Prevent an error by creating one
as necessary.

See: https://github.com/raspberrypi/firmware/issues/906

Signed-off-by: Phil Elwell <e888d2bd6f13f82caa51a37c03d034c76f661ba3@raspberrypi.org>

6by9/userland,JamesH65/userland,6by9/userland,raspberrypi/userland,JamesH65/userland,JamesH65/userland,6by9/userland,raspberrypi/userland,raspberrypi/userland