octeontx2-af: Physical link configuration support

CGX LMAC, the physical interface support link configuration parameters
like speed, auto negotiation, duplex  etc. Firmware saves these into
memory region shared between firmware and this driver.

This patch adds mailbox handler set_link_mode, fw_data_get to
configure and read these parameters.

Signed-off-by: Christina Jacob <cjacob@marvell.com>
Signed-off-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: Hariprasad Kelam <hkelam@marvell.com>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>