uboot-imx

ARM64: zynqmp: Add support to save env to FAT

Add support to save environment as a file of FAT filesystem
on to SD card. The file will be saved with name uEnv.txt.
This environment will be retrieved during boot.

Signed-off-by: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>