vfs: Convert qib_fs/ipathfs to use the new mount API

Convert the qib_fs/ipathfs 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.

[Q] Can qib_remove() race with qibfs_kill_super()?  Should qib_super
    accesses be serialised with some sort of lock?
[A] yes, it can and no, that's not the right solution.  See vfs.git #qibfs
    for an old attempt to handle that cleanly.  Infiniband folks were not
    interested...

Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
cc: Mike Marciniszyn <mike.marciniszyn@intel.com>
cc: linux-rdma@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>