soc: nordic: uicr: Populate UICR.VERSION field in gen_uicr.py

Set the VERSION field to 2.0 in gen_uicr.py to indicate the version of
the format the script produces blobs for. This is required for forwards
compatibility with newer versions of IronSide SE.

Signed-off-by: Jonathan Nilsen <jonathan.nilsen@nordicsemi.no>