net/bnxt: support Broadcom StrataGX

net/bnxt: support Broadcom StrataGX

This patch adds support for the Broadcom StrataGX® BCM5871X
series of Communications Processors.

These ARM based processors target a broad range of networking
applications including virtual CPE (vCPE) and NFV appliances,
10G service routers and gateways, control plane processing for
Ethernet switches, and network attached storage (NAS).

Other than adding the PCI Id for supporting the device,
the patch also adds a memory barrier before the Tx doorbell
and Completing ring doorbell is written to. Since ARM has a
weakly ordered memory model this enforces a strict ordering
of the descriptor writes before the doorbell writes happen.

Signed-off-by: John Carney <john.carney@broadcom.com>
Signed-off-by: Ajit Khaparde <ajit.khaparde@broadcom.com>