uboot-phytec

ts4800: update environment to boot with device tree

This commit updates the environment variables to be able to boot with a
device tree. The expected partition layout on the SD card is:
 - partition 1: type 0xDA, contains u-boot.bin
 - partition 2: type 0xC (fat), contains zImage and device tree
 - partition 3: type 0x83, root filesystem.

Signed-off-by: Damien Riegel <damien.riegel@savoirfairelinux.com>