staging: zcache: crypto API support

This patch allow zcache to use the crypto API for page compression.
It replaces the direct LZO compress/decompress calls with calls
into the crypto compression API. The compressor to be used is
specified in the kernel boot line with the zcache parameter like:
zcache=lzo or zcache=deflate.  If the specified compressor can't
be loaded, zcache uses lzo as the default compressor.

Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>