afs: Raise fake free space reporting

We report 'fake' values for free space, free file nodes, etc for the
'AFS' filesystem, since these values are not meaningful for AFS
itself. Currently we report about 9G of free space for most platforms,
and a few different values for a few others. Raise all of these to
2^32-1, so that trying to copy over 9G of data into AFS does not fail
for those applications that check the destination free space with
statfs(2). Note that one such application is KDE 4.8.x.

Consolidate all places that do this, and put the 'fake' value in one
place, AFS_VFS_FAKEFREE, along with the relevant comments.

Related issues reported by Lars Schimmer, Richard Brittain, and
others.

Change-Id: Ia15175da32744e11f62489c29bedfe1f5560d2b4
Reviewed-on: http://gerrit.openafs.org/9688
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Markus Koeberl <markus.koeberl@tugraz.at>
Tested-by: Markus Koeberl <markus.koeberl@tugraz.at>
Reviewed-by: D Brashear <shadow@your-file-system.com>