RDMA/bnxt_re: Fix incorrect DB offset calculation

To support host systems with non 4K page size, l2_db_size shall be
calculated with 4096 instead of PAGE_SIZE. Also, supply the host page size
to FW during initialization.

Signed-off-by: Devesh Sharma <devesh.sharma@broadcom.com>
Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>