Make sure SM violation IRQ is served

[jovanbulck]

SM violation IRQ (for debug purposes) doesn't always reliably fire. The signal should probably be buffered in the front-end for the remainder of the currently executing instruction.

[jovanbulck]

Update. Upon an exec_violation when jumping to a non-SM entry address, the violating instruction is still executed. The memory backbone component properly blocks any memory read/write operations, but instructions such as sancus_disable that do not touch memory still execute normally.

Solution. Block Sancus instructions in the execution unit upon sm_violation signal.