RDMA/bnxt_re: Use rdma_umem_for_each_dma_block()

This driver is taking the SGL out of the umem and passing it through a
struct bnxt_qplib_sg_info. Instead of passing the SGL pass the umem and
then use rdma_umem_for_each_dma_block() directly.

Move the calls of ib_umem_num_dma_blocks() closer to their actual point of
use, npages is only set for non-umem pbl flows.

Link: https://lore.kernel.org/r/0-v1-b37437a73f35+49c-bnxt_re_dma_block_jgg@nvidia.com


Acked-by: Selvin Xavier <selvin.xavier@broadcom.com>
Tested-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>