xilinx: versal: Add support for saving env based on bootmode

Enable saving variables to MMC(FAT) and SPI based on primary
bootmode. If bootmode is JTAG, dont save env anywhere(NOWHERE).

Enable ENV_FAT_DEVICE_AND_PART="0:auto" for Versal platforms as well.

Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>