Document the compatible strings for the BeagleV Ahead board which uses the T-Head TH1520 SoC. Link: https://beagleboard.org/beaglev-ahead Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> Reviewed-by: Guo Ren <guoren@kernel.org> Reviewed-by: Conor Dooley <conor.dooley@microchip.com> Signed-off-by: Drew Fustini <dfustini@baylibre.com> Signed-off-by: Conor Dooley <conor.dooley@microchip.com>