staging: nvec: add SPDX identifier.

It's good to have SPDX identifiers in all files to make it easier to
audit the kernel tree for correct licenses.

Fix up the staging nvec driver to have a proper SPDX identifiers, based
on the license text in the file itself.  The SPDX identifier is a
legally binding shorthand, which can be used instead of the full boiler
plate text.

This work is based on a script and data from Thomas Gleixner, Philippe
Ombredanne, and Kate Stewart.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Marc Dietrich <marvin24@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/nvec/nvec-keytable.h

+/* SPDX-License-Identifier: GPL-2.0+ */
 /*
  * drivers/input/keyboard/tegra-nvec.c
  *

drivers/staging/nvec/nvec.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * NVEC: NVIDIA compliant embedded controller interface
  *

drivers/staging/nvec/nvec.h

+/* SPDX-License-Identifier: GPL-2.0 */
 /*
  * NVEC: NVIDIA compliant embedded controller interface
  *

drivers/staging/nvec/nvec_kbd.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * nvec_kbd: keyboard driver for a NVIDIA compliant embedded controller
  *

drivers/staging/nvec/nvec_paz00.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * nvec_paz00: OEM specific driver for Compal PAZ00 based devices
  *

drivers/staging/nvec/nvec_power.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * nvec_power: power supply driver for a NVIDIA compliant embedded controller
  *

drivers/staging/nvec/nvec_ps2.c

+// SPDX-License-Identifier: GPL-2.0
 /*
  * nvec_ps2: mouse driver for a NVIDIA compliant embedded controller
  *