sys/targets: enable more syscall defines for freebsd
sys/targets: enable more syscall defines for freebsd

syzbot fails with:
error: use of undeclared identifier 'SYS___realpathat'
error: use of undeclared identifier 'SYS___realpathat'

google/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller