[SCSI] qla2xxx: Addition of shutdown callback handler.

This patch adds a shutdown handler to qla2xxx driver to make sure that all
DMA and firmware activities are stopped, and any associated driver resources
are released. The need for this handler arose when executing kexec in specific
environments caused the data of the 2nd kernel to be corrupted, due to DMA
activities.

Signed-off-by: Madhuranath Iyengar <Madhu.Iyengar@qlogic.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>