net: macb: add support for high speed interface

This patch adds support for 10GBASE-R interface to the linux driver for
Cadence's ethernet controller.
This controller has separate MAC's and PCS'es for low and high speed paths.
High speed PCS supports 100M, 1G, 2.5G, 5G and 10G through rate adaptation
implementation. However, since it doesn't support auto negotiation, linux
driver is modified to support 10GBASE-R instead of USXGMII.

Signed-off-by: Parshuram Thombare <pthombar@cadence.com>
Link: https://lore.kernel.org/r/1603975627-18338-1-git-send-email-pthombar@cadence.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>