scsi: megaraid_sas: reduce size of fusion_context and use vmalloc if kmalloc fails

Currently fusion context has fixed array load_balance_info. Use dynamic
allocation.  In few places, driver do not want physically contigious
memory.  Attempt to use vmalloc if physical contiguous memory is not
available.

Signed-off-by: Shivasharan S <shivasharan.srikanteshwara@broadcom.com>
Signed-off-by: Kashyap Desai <kashyap.desai@broadcom.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Tomas Henzl <thenzl@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>