Move screen saver stuff to x86 NOTES

[imp]

Summary

All the other architectures omit some or all of the screen savers from their
lint config. Move them to the x86 NOTES files and remove the exclusions. This
reduces slightly the number of savers sparc64 compiles, but since they are in
GENERIC, the overage is adequate and if someone reaelly wants to sort them out
in sparc64 they can sweat the details and the testing.

[imp]

Per jhb suggestion, combining with https://reviews.freebsd.org/D21233