NFS: Additional refactoring for fs_context conversion

Split out from commit "NFS: Add fs_context support."

This patch adds additional refactoring for the conversion of NFS to use
fs_context, namely:

 (*) Merge nfs_mount_info and nfs_clone_mount into nfs_fs_context.
     nfs_clone_mount has had several fields removed, and nfs_mount_info
     has been removed altogether.
 (*) Various functions now take an fs_context as an argument instead
     of nfs_mount_info, nfs_fs_context, etc.

Signed-off-by: Scott Mayhew <smayhew@redhat.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>