Rename zfs_* functions

Several functions were renamed when ZFS was originally ported to
Linux. Revert the code to the original names to minimize the
delta with upstream OpenZFS.

zfs_sb_teardown -> zfsvfs_teardown
zfs_sb_create -> zfsvfs_create
zfs_sb_setup -> zfsvfs_setup
zfs_sb_free -> zfsvfs_free
get_zfs_sb -> getzfsvfs
zfs_sb_hold -> zfsvfs_hold
zfs_sb_rele -> zfsvfs_rele

zfs_sb_prune_aliases  -> zfs_prune_aliases (Linux-only)
zfs_sb_prune -> zfs_prune (Linux only)

Align the zfs_vnops.h and zfs_vfsops.h with upstream as much
as possible. Several prototypes were removed and those that
remain were reordered.

Move the EXPORT_SYMBOL lines to the end of the source files
for consistency with the other source files.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>