Windows: Move AFSVolume functions to new file

Windows: Move AFSVolume functions to new file

In an effort to declutter AFSFcbSupport.cpp, move AFSVolume
functions to a new source file, AFSVolume.cpp.

Change-Id: I663352d7bc4004c41bbab55fdf5bd8e36b373cf9
Reviewed-on: http://gerrit.openafs.org/9697
Reviewed-by: Peter Scott <pscott@kerneldrivers.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Tested-by: Jeffrey Altman <jaltman@your-file-system.com>