boot.scr is a u-boot script that loads and execute ubldr.bin
If not present u-boot will automatically boot loader.efi which
is already installed.
This means that all armv6/armv7 images are now booted via EFI
Tested-On: RPI-B
Tested-On: RPI2
Tested-On: OrangePi One
Tested-On: All lot of other boards
MFC after: Never
Relnotes: yes
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