net, thunder, bgx: Add support to get MAC address from ACPI.

Currently there is no way to get the MAC address in a firmware
independent manner, so set the MAC address of the device directly from
the ACPI tables.

The binding agrees with the proposed standard here:

http://www.uefi.org/sites/default/files/resources/nic-request-v2.pdf



Based on code from: Narinder Dhillon <ndhillon@cavium.com>
                    Tomasz Nowicki <tomasz.nowicki@linaro.org>
                    Robert Richter <rrichter@cavium.com>

Signed-off-by: Tomasz Nowicki <tomasz.nowicki@linaro.org>
Signed-off-by: Robert Richter <rrichter@cavium.com>
Signed-off-by: David Daney <david.daney@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>