Restore PPS_SYNC in NOTES

This partially reverts e81e77c5a055, leaving the option both in
GENERICs on amd64/arm64/arm, and in global NOTES file. Apparently
this better matches existing practice, where we do not try to hard
to make LINT and GENERIC complimentary.

Requested and reviewed by: jhb
Sponsored by: The FreeBSD Foundation
MFC after: 1 week