RDMA/bnxt_re: Add bnxt_re driver build support

Makefile and Kconfig changes for enabling bnxt_re compilation

Signed-off-by: Devesh Sharma <devesh.sharma@broadcom.com>
Signed-off-by: Somnath Kotur <somnath.kotur@broadcom.com>
Signed-off-by: Sriharsha Basavapatna <sriharsha.basavapatna@broadcom.com>
Signed-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Reviewed-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>