arm64: dts: mt8173: Fix nor_flash node

Add axi clock since the driver change to DMA mode which need
to enable axi clock. And change spi clock to 26MHz as default.

Signed-off-by: Xiangsheng Hou <xiangsheng.hou@mediatek.com>
Link: https://lore.kernel.org/r/20220630090157.29486-2-xiangsheng.hou@mediatek.com


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>