realtek: generate compat_version 2.0 for GS1900

realtek: generate compat_version 2.0 for GS1900

The GS1900 images have been updated to have a larger firmware partition,
bumping the compatibility version to 2.0. However, since this version is
generated on first boot and the default was used, these images still
advertised 1.0 after a fresh install.

Add a new uci-defaults script that will generate the correct version for
all affected Zyxel GS1900 devices.

Fixes: 35acdbe9095d ("realtek: merge Zyxel GS1900 firmware partitions")
Signed-off-by: Sander Vanheule <sander@svanheule.net>