dt-bindings: riscv: Add BeagleV Ahead board compatibles

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>

Documentation/devicetree/bindings/riscv/thead.yaml

@@ -17,6 +17,10 @@ properties:
     const: '/'
   compatible:
     oneOf:
+      - description: BeagleV Ahead single board computer
+        items:
+          - const: beagle,beaglev-ahead
+          - const: thead,th1520
       - description: Sipeed Lichee Pi 4A board for the Sipeed Lichee Module 4A
         items:
           - enum: