arm64: dts: allwinner: h6: tanix-tx6: enable emmc

Tanix TX6 has 32 GiB eMMC. Add a node for it.

Signed-off-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20210722161220.51181-4-jernej.skrabec@gmail.com