iot2050: Add script for signing artifacts

There are many ways to get a signed firmware for the IOT2050 devices,
namely for the parts under user-control. This script documents one way
of doing it, given a signing key. Augment the board documentation with
the required procedure around it.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
2 files changed