[ceca] Report number of correctly guessed key byte differences
[ceca] Report number of correctly guessed key byte differences

This number is actually a far more relevant indicator for the amount of
leakage in the traces than successful key recovery (pass/fail). This
commit therefore adds the functionality to compute this number and
report it on the command line.

This addresses lowRISC/ot-sca#30.

Signed-off-by: Pirmin Vogel <386a7fc8e7338ed7899b4d9883c0ebec5de81366@lowrisc.org>

lowRISC/ot-sca,lowRISC/ot-sca