block: IBM RamSan 70/80 fixes inconsistent locking.

This patch includes changes to the cregs locking scheme. Before,
inconsistant locking would occur because of misuse of spin_lock,
spin_lock_bh, and counter parts.

Signed-off-by: Philip J Kelleher <pjk1939@linux.vnet.ibm.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>