[SCSI] zfcp: Replace kmem_cache for "status read" data

zfcp requires a mempool for the status read data blocks to resubmit
the "status read" requests at any time. Each status read data block
has the size of a page (4096 bytes) and needs to be placed in one
page.

Instead of having a kmem_cache for allocating page sized chunks, use
mempool_create_page_pool to create a mempool returning pages and
remove the zfcp kmem_cache.

Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: Steffen Maier <maier@linux.vnet.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>