dt: net: add DWC EQoS binding

dt: net: add DWC EQoS binding

The Synopsys DWC EQoS is a configurable Ethernet MAC/DMA IP block which
supports multiple options for bus type, clocking and reset structure, and
feature list.

This patch imports the binding from the Linux kernel, including my V3
patch to extend the binding to cover the Tegra186, which is applied for
next-20160912. So far, my changes have been acked by Lars Persson, the
original author of the binding.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>