Add: BeagleBoard.org repository

Add extrepo entry for BeagleBoard.org repository.

Reference:

• https://www.beagleboard.org/distros
• https://github.com/beagleboard/repos-armhf
• https://github.com/beagleboard/repos-arm64
• https://github.com/beagleboard/repos-riscv64

Signed-off-by: Kurva Prashanth krvprashanth@riseup.net