net: phy: add TI DP83869HM ethernet driver

This driver is based on an older downstream TI kernel, with
changes and cleanups to work with mainline device-tree bindings.

Signed-off-by: Dominic Rath <rath@ibv-augsburg.net>
Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>