Staging: ramzswap: Remove backing swap support

Currently, each ramzswap device can be assigned
a separate 'backing swap' file/partition. The ramzswap
driver forwards swap I/O requests to this backing swap
whenever an incompressible page is found.

This feature adds nearly 700 lines of code and it
also duplicates much of the swapon() functionality
(for example, finding swap extents and so on). Removing
this code makes the driver much simpler and should
help its transition from staging to stable drivers
area (drivers/block/).

Similar functionality may be implemented if we can
implement migrating pages across swap devices but the
details have not yet been worked out.

Support for _partitions_ as backing swap could be
retained as it requires a few lines of code only.
This part can be re-introduced later if above swap
migration method turns out to be infeasible.

More cleanups and code comments will be added soon.

Signed-off-by: Nitin Gupta <ngupta@vflare.org>
Acked-by: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>