RDMA/bnxt_re: Use correct sizing on buffers holding page DMA addresses

umem->nmap is used while allocating internal buffer for storing
page DMA addresses. This causes out of bounds array access while iterating
the umem DMA-mapped SGL with umem page combining as umem->nmap can be
less than number of system pages in umem.

Use ib_umem_num_pages() instead of umem->nmap to size the page array.
Add a new structure (bnxt_qplib_sg_info) to pass sglist, npages and nmap.

Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>