zswap: allow initialization at boot without pool

zswap: allow initialization at boot without pool

Allow zswap to initialize at boot even if it can't create its pool due
to a failure to create a zpool and/or compressor.  Allow those to be
created later, from the sysfs module param interface.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Dan Streetman <[email protected]>
Cc: Seth Jennings <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Sergey Senozhatsky <[email protected]>
Cc: Minchan Kim <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>