Update ICache testplan after review meeting
Update ICache testplan after review meeting

I think these represent the test cases we discussed. I've also removed
non-existent entries from the "tests" keys: I didn't really understand
how dvsim.py worked when I wrote the original version and they just
cause irritating warnings.

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