arm64: dts: armada-3720-turris-mox: fixed indices for the SDHC controllers

Since drivers/mmc/host/sdhci-xenon.c declares the PROBE_PREFER_ASYNCHRONOUS
probe type, it is not guaranteed whether /dev/mmcblk0 will belong to
sdhci0 or sdhci1. In turn, this will break booting by:

root=/dev/mmcblk0p1

Fix the issue by adding aliases so that the old MMC controller indices
are preserved.

Fixes: 7320915c ("mmc: Set PROBE_PREFER_ASYNCHRONOUS for drivers that existed in v4.14")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>