[dv] Small core_ibex_test_lib refactor
[dv] Small core_ibex_test_lib refactor

Splits out checking for IRQ handling and waiting for specific xRET to
seperate tasks to allow more flexible checking.

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