Controller FSM: simplify `debug_mode_q`-related control
Controller FSM: simplify `debug_mode_q`-related control

The FSM now uses input signals for interrupt and debug request handling
that depend on whether the core is in debug mode. This avoids the need
for many `debug_mode_q` guards and somewhat simplifies the FSM.

If in debug mode, the core shall not handle interrupts according to the
spec anyway.

AmbiML/ibex,AmbiML/ibex,lowRISC/ibex,lowRISC/ibex,AmbiML/ibex,lowRISC/ibex,lowRISC/ibex,AmbiML/ibex