autofs/autofs4: Move compat_ioctl handling into fs

Handling of autofs ioctl numbers does not need to be generic
and can easily be done directly in autofs itself.

This also pushes the BKL into autofs and autofs4 ioctl
methods.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Ian Kent <raven@themaw.net>
Cc: Autofs <autofs@linux.kernel.org>
Cc: John Kacur <jkacur@redhat.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>