scsi: megaraid_sas: use vmalloc for crash dump buffers and driver's local RAID map

Driver's local RAID map is accessed frequently. We will first try to get
memory from __get_free_pages. If this fails, fall back to using vmalloc.
For crash dump buffers always prefer vmalloc.

Signed-off-by: Kashyap Desai <kashyap.desai@broadcom.com>
Signed-off-by: Shivasharan S <shivasharan.srikanteshwara@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>