pico-imx7d: Add fastboot support
fastboot tool is a convenient way to flash the eMMC, so
add support for it.
Examples of usages:
On the pico-imx7d U-Boot prompt:
=> fastboot 0
On the Linux PC connected via USB:
1. Retrieving the U-Boot version
$ sudo fastboot getvar bootloader-version -i 0x0525
bootloader-version: U-Boot 2018.07-rc1-03888-gde846f9
finished. total time: 0.000s
2. Resetting the board
$ sudo fastboot reboot -i 0x0525
(this causes the pico-imx7d to reboot)
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>