Implement AUE_PREAD and AUE_PWRITE BSM conversion support, eliminating
console warnings when pread(2) and pwrite(2) are used with full
system-call auditing enabled. We audit the same file-descriptor data
for these calls as we do read(2) and write(2).

Approved by: re (kib)
MFC after: 3 days
Sponsored by: DARPA, AFRL