Add kern_vm_mmap2(), kern_vm_mprotect(), kern_vm_msync(), kern_vm_munlock(),
kern_vm_munmap(), and kern_vm_madvise(), and use them in various compats
instead of their sys_*() counterparts.

Reviewed by: ed, dchagin, kib
MFC after: 2 weeks
Sponsored by: DARPA, AFRL
Differential Revision: https://reviews.freebsd.org/D9378