[util, gen-otp-img] Add random seed as arg
[util, gen-otp-img] Add random seed as arg

A single external arg `--seed` is added to the
`util/design/gen-otp-img.py` tool to make it generate OTP images
deterministically with an externally provided seed.

The individual seed override controls for image, OTP and LC are still
operational.

Signed-off-by: Srikrishna Iyer <2803d640feace36379942447842f26c7747b4dc3@google.com>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan