RISC-V: Add BeagleV Starlight Beta device tree

Add initial device tree for the BeagleV Starlight Beta board. About 300
of these boards were sent out as part of a now cancelled BeagleBoard.org
project.

I2C timing data is based on the device tree in the vendor u-boot port.
Heartbeat LED added by Geert.

Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Co-developed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>