ARM64: zynqmp: Enable fastboot for first SD/MMC/EMMC device

ARM64: zynqmp: Enable fastboot for first SD/MMC/EMMC device

DNL numbers are not changed that's why fastboot needs to be called with
-i parameter (Xilinx vendor id).

- Show available devices
sudo fastboot -i 0x03fd devices
xilinx_zynqmp_zcu100	fastboot

- Stop fastboot and go back to U-Boot prompt
sudo fastboot -i 0x03fd continue

- Reboot the board
sudo fastboot -i 0x03fd reboot

- Get internal variables
sudo fastboot -i 0x3fd getvar bootloader-version
bootloader-version: U-Boot 2016.07-00026-g19bd53044817
sudo fastboot -i 0x3fd getvar downloadsize
downloadsize: 0x06000000
sudo fastboot -i 0x3fd getvar version
version: 0.4
(regular variables needs to have fastboot. prefix - there is also
serialno variable which should be define as serial#)

- Format SD/MMC/EMMC card
sudo fastboot -i 0x3fd oem format
- Write images to boot and Linux partition
sudo fastboot -i 0x3fd flash boot sd.img
sudo fastboot -i 0x3fd flash Linux os.img

- Creating sd.img or os.img
$ dd if=/dev/zero of=sd.img bs=1024 count=1024
$ mkfs.vfat sd.img
$ mkdir sd-mount
$ mount -o loop sd.img sd-mount
$ echo foo > sd-mount/bar
$ umount sd-mount

partitions setting should be checked by running gpt command.

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