makefs: make the buffer functions look exactly like the kernel ones

From NetBSD christos Sat Jan 26 00:19:39 2013 +0000

make the buffer functions look exactly like the kernel ones and add other
cruft to make the kernel files compile.

ffs.c 1.54
ffs/buf.c 1.13
ffs/buf.h 1.3
ffs/ffs_alloc.c 1.21
ffs/ffs_balloc.c 1.15

Reviewed by: marcel, ngie
Obtained from: NetBSD
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D8404