vfs: Convert coda to use the new mount API

Convert the coda filesystem to the new internal mount API as the old
one will be obsoleted and removed.  This allows greater flexibility in
communication of mount parameters between userspace, the VFS and the
filesystem.

See Documentation/filesystems/mount_api.txt for more information.

Note this is slightly tricky as coda currently only has a binary mount data
interface.  This is handled through the parse_monolithic hook.

Also add a more conventional interface with a parameter named "fd" that
takes an fd that refers to a coda psdev, thereby specifying the index to
use.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Jan Harkes <jaharkes@cs.cmu.edu>
cc: coda@cs.cmu.edu
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>