aes-390x.pl: commentary update.

#

# Add support for hardware AES192/256 and reschedule instructions to

# minimize/avoid Address Generation Interlock hazard and to favour

# dual-issue z10 pipeline. This gave ~25% improvement on z10. The gain

# should be larger on earlier CPUs, because being dual-issue z10 makes

# it improssible to eliminate the interlock condition, critial path is

# not long enough. Yet z10 spends ~24 cycles per byte processed with

# 128-bit key.

# dual-issue z10 pipeline. This gave ~25% improvement on z10 and

# almost 50% on z9. The gain is smaller on z10, because being dual-

# issue z10 makes it improssible to eliminate the interlock condition:

# critial path is not long enough. Yet it spends ~24 cycles per byte

# processed with 128-bit key.

#

# Unlike previous version hardware support detection takes place only

# at the moment of key schedule setup, which is denoted in key->rounds.