Rewrite completely uEnv.txt

[F5OEO]

uboot environment variables is different across boards which is hard to maintain. Writing an universal env could be very usefull to extended capabilities (multi-boot, usb boot ...) and could be used over all models.

[VasylSamoilov]

Question: does uEnv.txt have any effect when booting full raspbian (kuiper linux)? Because right now it works pretty good with the following uEnv.txt:
adi_sdboot=echo Copying Linux from SD to RAM... && fatload mmc 0 0x3000000 ${kernel_image} && fatload mmc 0 0x2A00000 ${devicetree_image} && if fatload mmc 0 0x2000000 ${ramdisk_image}; then bootm 0x3000000 0x2000000 0x2A00000; else bootm 0x3000000 - 0x2A00000; fi bootargs=console=ttyPS0,115200 root=/dev/mmcblk0p2 rw earlycon rootfstype=ext4 rootwait clk_ignore_unused cpuidle.off=1