Removal of todo's and currently unused logic

Created by: silabs-oysteink

Removed logic intended for preserving address of a faulted load or store for use in mtval CSR.

This code was not used, and it would not work in the current state as it could overwrite the faulted address.

Added assertion to check max number of retired instructions after an NMI becomes pending. This uncovered a case where the result of a faulted load may actually be used.

Bugfix: Halting ID stage in the same cycle as the bus error arrives, allowing max 1 extra retirement after the faulted LSU instruction..

Non-SEC due to the bugfix.

Signed-off-by: Oystein Knauserud Oystein.Knauserud@silabs.com