Allow PT_INTERP and PT_NOTES segments to be located anywhere in the
executable image. Keep one page (arbitrary) limit on the max allowed
size of the PT_NOTES.

The ELF image activators still require that program headers of the
executable are fully contained in the first page of the image file.

Reviewed by: emaste, jhb
Sponsored by: The FreeBSD Foundation
MFC after: 2 weeks
Differential revision: https://reviews.freebsd.org/D3871