arch: dts: am642-sk-u-boot: Disable main_sdhci0 DT node and define alias index...

arch: dts: am642-sk-u-boot: Disable main_sdhci0 DT node and define alias index 1 for main_sdhci1 node

A Wilink wireless device is connected to MMCSD0 subsystem and is not
supported in U-Boot. Therefore, disable main_sdhci0 device tree node in
U-Boot.

If main_sdhci0 device tree node is disabled then the the index of
main_sdhci1 node becomes 0 which leads to break in boot flow. Therefore,
add an alias to fix the index to 1.

Signed-off-by: Aswath Govindraju <a-govindraju@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Link: https://lore.kernel.org/r/20210726152807.22991-3-a-govindraju@ti.com