[rv_core_ibex] Add assertion for icache scramble key request after FENCE.I
[rv_core_ibex] Add assertion for icache scramble key request after FENCE.I

Signed-off-by: Andreas Kurth <62c4a7f75976b7a2fb8d79afddaccc3e9236aad5@lowrisc.org>

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