wandboard: Pass mmc aliases

wandboard: Pass mmc aliases

Originally, the mmc aliases node was present in imx6qdl-wandboard.dtsi.

After the sync with Linux in commit d0399a46e7cd ("imx6dl/imx6qdl:
synchronise device trees with linux"), the aliases node is gone as
the upstream version does not have it.

This causes a regression in which the SD card cannot be found anymore:

Since commit  the aliases node has been removed
U-Boot 2022.10-00999-gcca41ed3d63f-dirty (Nov 03 2022 - 22:07:38 -0300)

CPU:   Freescale i.MX6QP rev1.0 at 792 MHz
Reset cause: POR
DRAM:  2 GiB
Core:  62 devices, 17 uclasses, devicetree: separate
PMIC:  PFUZE100 ID=0x10
MMC:   FSL_SDHC: 0, FSL_SDHC: 1, FSL_SDHC: 2
Loading Environment from MMC... MMC: no card present
*** Warning - No block device, using default environment

Fix it by passing the alias node in the u-boot.dtsi file to
restore the original behaviour where the SD card (esdhc3) was
mapped to mmc0.

Fixes: d0399a46e7cd ("imx6dl/imx6qdl: synchronise device trees with linux")
Signed-off-by: Fabio Estevam <festevam@denx.de>