zcache: s/int/bool/ on the various options.

There are so many, but this allows us to at least have them
right in as bool.

Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>
[v1: Rebase on ramster->zcache move]
[v2: Rebase on staging/zcache: Fix/improve zcache writeback code, tie to a config option]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>