* gnu/bootloader/u-boot.scm (u-boot-banana-pi-m2-ultra-bootloader): New
exported variable.
(install-allwinner-u-boot): New variable.
(u-boot-allwinner-bootloader): New variable.
* gnu/packages/bootloaders.scm (u-boot-banana-pi-m2-ultra): New exported
variable.
* gnu/system/install.scm (banana-pi-m2-ultra-installation-os): New exported
variable.