Fix IF stalls preventing deassertion of regfile write enable (#222)
Fix IF stalls preventing deassertion of regfile write enable (#222)

* ID stage: make single-cycle instr clear `instr_multicycle_done_q`

Previously, this signal was only cleared when starting the next
multi-cycle instruction.

* ID stage: only eval `instr_multicycle_done_q` for multi-cycle instr

This signal should only be evaluated if the ID/EX stage currently
executes a multi-cycle instruction. Without this commit, the signal
is also evaluated for single-cycle instructions and can for example
cause the register file write enable to not be de-asserted in case of
stalls in the IF stage.

This bug was repored by @udinator. This resolves lowrisc/ibex#216.

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