helper functions
================
These functions focus on supporting the arm-sdk and generating and writing the appropriate images to different block devices.

## build_atf()
## build_uboot()
## set-bootloader()
## bootloader-sd-version()
## upgrade-sd-bootloader()
## erase-sd-bootloader()
## create_spi_image()
## spi_flash_img()
## erase-spi-flash()
## write-spi-flash()
## write-emmc-flash()
## create-u-boot-menu()
## create-u-boot-spi-scripts()
"$R/tmp/kernels/u-boot-rockpro64"/scripts/load-spi-from-usb.cmd
"$R/tmp/kernels/u-boot-rockpro64"/scripts/flash-spi.cmd
"$R/tmp/kernels/u-boot-rockpro64"/scripts/erase_spi.cmd
## create-rockpro64-scripts()
/usr/local/sbin/rockpro64_reset_spi_flash.sh
/usr/local/sbin/rockpro64_reset_emmc.sh
/usr/local/sbin/rockpro64_disable_otg.sh
/usr/local/sbin/rockpro64_enable_eth_gadget.sh