scsi: mpt3sas: Separate out RDPQ allocation to new function

For readability separate out RDPQ allocations to new function
base_alloc_rdpq_dma_pool().

Link: https://lore.kernel.org/r/1587626596-1044-4-git-send-email-suganath-prabu.subramani@broadcom.com


Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Suganath Prabu <suganath-prabu.subramani@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>