Add encrypt+authenticate modes to cryptotest tool

Like jhb's cryptocheck (uncommitted so far), express encrypt+authenticate
modes as "-a <encalg>+<authalg>".

Example use with aesni(4) on AMD Zen family:

$ ./cryptotest -d aesni0 -a aes256 10000 $((128*1024))

2.331 sec,   20000 aes256       crypts,  131072 bytes, 1124707930 byte/sec,  8580.8 Mb/sec

$ ./cryptotest -d aesni0 -a sha256 10000 $((128*1024))

1.109 sec,   10000 sha256       crypts,  131072 bytes, 1181577161 byte/sec,  9014.7 Mb/sec

$ ./cryptotest -d aesni0 -a aes256+sha256 10000 $((128*1024))

3.805 sec,   10000 sha256+aes256 crypts,  131072 bytes, 344460116 byte/sec,  2628.0 Mb/sec

Reported by: jhb
Sponsored by: Dell EMC Isilon