gpio: rcar: Add DT binding for r8a77990

Add compatible string for R-Car E3 (r8a77990) in gpio-rcar.
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/devicetree/bindings/gpio/renesas,gpio-rcar.txt

@@ -17,6 +17,7 @@ Required Properties:
     - "renesas,gpio-r8a7796": for R8A7796 (R-Car M3-W) compatible GPIO controller.
     - "renesas,gpio-r8a77965": for R8A77965 (R-Car M3-N) compatible GPIO controller.
     - "renesas,gpio-r8a77970": for R8A77970 (R-Car V3M) compatible GPIO controller.
+    - "renesas,gpio-r8a77990": for R8A77990 (R-Car E3) compatible GPIO controller.
     - "renesas,gpio-r8a77995": for R8A77995 (R-Car D3) compatible GPIO controller.
     - "renesas,rcar-gen1-gpio": for a generic R-Car Gen1 GPIO controller.
     - "renesas,rcar-gen2-gpio": for a generic R-Car Gen2 or RZ/G1 GPIO controller.