add support for software crypto to allow WPA/WPA2/RSN. it is disabled

add support for software crypto to allow WPA/WPA2/RSN.  it is disabled
for now because it needs more testing, but basic WPA/WPA2 and WEP
seems to work.  to enable it, set the compiled-in ath_softcrypto
variable to 1.

this is based on a previous diff from damien@ with some changes to
disable the hardware crypto engine if softcrypto is enabled and to
keeps the hardware crypto code in place to allow later work on
hardware WPA/WPA2.