drivers: gpio: amd8111: use SPDX-License-Identifier

Prefer SPDX-License-Identifier over hand-written texts.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Link: https://lore.kernel.org/r/20201203182423.5499-3-info@metux.net


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>