dt-bindings: net: dp8386x: Add MIT license along with GPL-2.0

dt-bindings: net: dp8386x: Add MIT license along with GPL-2.0

Modify license to include dual licensing as GPL-2.0-only OR MIT
license for TI specific phy header files. This allows for Linux
kernel files to be used in other Operating System ecosystems
such as Zephyr or FreeBSD.

While at this, update the GPL-2.0 to be GPL-2.0-only to be in sync
with latest SPDX conventions (GPL-2.0 is deprecated).

While at this, update the TI copyright year to sync with current year
to indicate license change.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Trent Piepho <tpiepho@impinj.com>
Cc: Wadim Egorov <w.egorov@phytec.de>
Cc: Kip Broadhurst <kbroadhurst@ti.com>
Signed-off-by: Udit Kumar <u-kumar1@ti.com>
Acked-by: Wadim Egorov <w.egorov@phytec.de>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>