dt-bindings: spi: add mt8192-nor compatible string

Add MT8192 spi-nor controller support.

Signed-off-by: Ikjoon Jang <ikjn@chromium.org>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20201006155010.v5.1.I4cd089ef1fe576535c6b6e4f1778eaab1c4441cf@changeid


Signed-off-by: Mark Brown <broonie@kernel.org>