doc: board: renesas: Document Renesas Gray Hawk board support

Document support for Renesas Gray Hawk Single development board
based on Renesas R-Car V4M (R8A779H0) SoC.

Fixes: 53066deccbed ("ARM: renesas: Add Renesas R8A779H0 V4M Gray Hawk board code")
Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>

doc/board/renesas/renesas.rst

diff --git a/doc/board/renesas/renesas.rst b/doc/board/renesas/renesas.rst
index b145c2c..7673a3e 100644
--- a/doc/board/renesas/renesas.rst
+++ b/doc/board/renesas/renesas.rst
@@ -192,6 +192,12 @@
      - arm64
      - r8a779g3_sparrowhawk_defconfig
 
+   * -
+     - Gray Hawk
+     - R8A779H0 (V4M)
+     - arm64
+     - r8a779h0_grayhawk_defconfig
+
    * - RZ/G2 Family
      - Beacon EmbeddedWorks RZ/G2M SoM
      - R8A774A1 (RZ/G2M)