arm64: renesas: document Eagle board bindings

Document the Eagle device tree bindings, listing it as a supported board.

This allows to use checkpatch.pl to validate .dts files referring to the
Eagle board.
Signed-off-by: NSergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NSimon Horman <horms+renesas@verge.net.au>

Documentation/devicetree/bindings/arm/shmobile.txt

@@ -59,6 +59,8 @@ Boards:
     compatible = "renesas,bockw", "renesas,r8a7778"
   - Draak (RTP0RC77995SEB0010S)
     compatible = "renesas,draak", "renesas,r8a77995"
+  - Eagle (RTP0RC77970SEB0010S)
+    compatible = "renesas,eagle", "renesas,r8a77970"
   - Genmai (RTK772100BC00000BR)
     compatible = "renesas,genmai", "renesas,r7s72100"
   - GR-Peach (X28A-M01-E/F)