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>
1 file changed