RDMA/bnxt_re: Add bnxt_re RoCE driver

This patch introduces the RoCE driver for the
Broadcom NetXtreme-E 10/25/50/100/200G RoCE HCAs.

The RoCE driver is a two part driver that relies
on the bnxt_en NIC driver to operate. The changes
needed in the bnxt_en driver is included through
another patch "L2-RoCE driver communication interface"
in this set.

Presently, There is no user space support, Hence
recommendation to use the krping kernel module for
testing. User space support will be incorporated in
subsequent patch submissions.

Reviewed by: imp
Approved by: imp
Differential revision: https://reviews.freebsd.org/D45011

(cherry picked from commit acd884dec99adcf8c4cdd0aa8a50be79c216f8e8)