dt-bindings: riscv: add starfive jh7100 bindings

Add DT binding documentation for the StarFive JH7100 Soc [1] and the
BeagleV Starlight JH7100 board [2].

[1] https://github.com/starfive-tech/beaglev_doc
[2] https://github.com/beagleboard/beaglev-starlight



Signed-off-by: Drew Fustini <drew@beagleboard.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>