dt-bindings: net: dp83869: Add TI dp83869 phy

Add dt bindings for the TI dp83869 Gigabit ethernet phy
device.

Signed-off-by: Dan Murphy <dmurphy@ti.com>
CC: Rob Herring <robh+dt@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>