[otbn,dv] Add a check that we don't call run_otbn() in reset
[otbn,dv] Add a check that we don't call run_otbn() in reset

This is a sign that something has gone wrong elsewhere in the
testbench and gives a nice quick, easy-to-understand message about
what's happened.

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

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