dt-bindings: mtd: mtk-quadspi: update bindings for MT7629 SoC

This updates bindings for the MT7629 SPI-NOR controller.

Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Boris Brezillon <bbrezillon@kernel.org>