[otbn,rtl] Only handle RMA request if strictly Mubi-true
[otbn,rtl] Only handle RMA request if strictly Mubi-true

OTBN should only handle a Mubi-encoded RMA request if it is strictly
true, thereby reducing the potential for FI on RMA requests.  OTBN
already detected Mubi-invalid RMA requests and would lock if such a
(likely tampered) request is detected.  This commit only adds another
safety net to this mechanism.

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

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