staging: fsl-dpaa2/eth: add SPDX license identifiers

The DPAA2 Ethernet driver files use a GPL-2.0+ OR BSD-3-Clause
license. Add SPDX tags and delete the full license text,
keeping the existing licenses for each file.
Add a GPL-2.0 tag for the Makefile.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>