include: add SPDX GPL-2.0-only license tags where applicable ...

Interpret "GPLv2" as "GPLv2 only".

Signed-off-by: Roland Hieber <rohieb@rohieb.name>
Reviewed-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

of/net: Add net related of helpers ...

of_get_phy_mode to parse the phy mode from the devicetree and
of_get_mac_address to parse a MAC address from the devicetree.
Directly taken from the Kernel.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>