[otbn,util] Fix run-some.py when destdir doesn't lie in project
[otbn,util] Fix run-some.py when destdir doesn't lie in project

The "run the testbench" command runs inside destdir. It needs to know
where to find the ISS, which it would normally do by searching up for
a .git from the current directory. Setting the REPO_TOP environment
variable overrides this behaviour and tells it where to look.

Signed-off-by: Rupert Swarbrick <290093e2ad2515ed2f14d749293c8cf8e02ca274@lowrisc.org>

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