[rv_core_ibex, rtl] Add local escalation path to disable fetch
[rv_core_ibex, rtl] Add local escalation path to disable fetch

When a major core error is seen the local escalation path immediately
shuts down fetch enable in addition to raising a fatal alert.

Signed-off-by: Greg Chadwick <3e4c3d6d87c017d1a2fa161477653b4039c6b2fb@lowrisc.org>

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