dt-bindings: riscv: update microchip.yaml's maintainership

Daire and I are the platform maintainers for Microchip's RISC-V
FPGAs. Update the maintainers in microchip.yaml to reflect this and
explicitly add the binding to the SoC's MAINTAINERS entry.

Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20221010221704.2161221-3-conor@kernel.org/


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>