[otbn,rtl] Clear INSN_CNT on a lifecycle escalation signal
[otbn,rtl] Clear INSN_CNT on a lifecycle escalation signal

We document that this register will always read as zero when OTBN is
locked. Make it so!

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

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