ARM64: dts: meson-axg: enable the eMMC controller

The IP of eMMC controller in AXG is similiar to Meson-GX series.
Here we add the initial support of the HS200 mode with
clock running at 166MHz (to be safe), since we found some eMMC chip
fail to run at 200MHz due to tunning phase error.

Signed-off-by: Nan Li <nan.li@amlogic.com>
Signed-off-by: Yixun Lan <yixun.lan@amlogic.com>
[khilman: drop incorrect SDIO pwrseq property]
Signed-off-by: Kevin Hilman <khilman@baylibre.com>