arm64: dts: allwinner: h6: tanix: Add MMC1 node

Both, Tanix TX6 and Tanix TX6 mini, have SDIO wifi module, albeit
different. However, driver can be autoprobed via SDIO ID.

Add MMC1 node, so kernel can discover wifi module and load driver for
it.

Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>