hpfs: remove the BKL

This removes the BKL in hpfs in a rather awful
way, by making the code only work on uniprocessor
systems without kernel preemption, as suggested
by Andi Kleen.

The HPFS code probably has close to zero remaining
users on current kernels, all archeological uses of
the file system can probably be done with the significant
restrictions.

The hpfs_lock/hpfs_unlock functions are left in the
code, sincen Mikulas has indicated that he is still
interested in fixing it in a better way.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Andi Kleen <ak@linux.intel.com>
Cc: Mikulas Patocka <mikulas@artax.karlin.mff.cuni.cz>
Cc: linux-fsdevel@vger.kernel.org