smegw01: Enable EMMC boot from multiple partitions

smegw01: Enable EMMC boot from multiple partitions

GPT Partition labels are used for determining the right
root filesystem to boot from.

The U-Boot environment is configured to reside in the eMMC hardware
boot partition we are currently booted from.

This should enable a dual copy approach for upgrading the bootloader.
One can overwrite the inactive hardware partition with new bootloader
and environment and afterwards switch the eMMC boot partition for an
atomic bootloader switch.

Signed-off-by: Eduard Strehlau <eduard@lionizers.com>
Signed-off-by: Fabio Estevam <festevam@denx.de>