freebsd32: Remove mac_syscall from the unimpl list

The mac_syscall system call works fine as long as any MAC module
that provides a mpo_syscall method handles compat32 appropriately.

Regenerate system call files for freebsd32.

Reviewed by: sjg
Obtained from: Juniper Networks, Inc.
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D41575