Generate images for Allwinner-based boards

[obbardc]

Not yet implemented.

[obbardc]

To do this we need to have an action to install the bootloader to the SD card.

This should be done after the image is created as blank but before the partition table is created.

[obbardc]

Some boards (Raspberry pi and Beaglebone are OK) need a small bootloader SPL writing to the SD card image before the rootfs has been initialised, in the space between the partition table and the partition header.

this is tricky as we can't just package the bootloader SPL up in a deb package as we can with the kernel.

I think the best way is for pdk-mediagen to include a known-good binary version of the bootloader SPL directly in the GIT repository.

the rest of the process of generating the image is no different.