RDMA/erdma: Add the hardware related definitions

ERDMA is a PCIe device, and this file provides ERDMA hardware related
definitions, mainly including PCIe device capabilities and restrictions,
device registers definitions, doorbell space, doorbell structure
definitions and WQE definitions.

Link: https://lore.kernel.org/r/20220727014927.76564-3-chengyou@linux.alibaba.com
Signed-off-by: Cheng Xu <chengyou@linux.alibaba.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>