ARM: shmobile: Document RZ/G1H SoC DT binding

Document the RZ/G1H (r8a7742) SoC.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

Documentation/devicetree/bindings/arm/shmobile.txt

@@ -13,6 +13,8 @@ SoCs:
     compatible = "renesas,r8a73a4"
   - R-Mobile A1 (R8A77400)
     compatible = "renesas,r8a7740"
+  - RZ/G1H (R8A77420)
+    compatible = "renesas,r8a7742"
   - RZ/G1M (R8A77430)
     compatible = "renesas,r8a7743"
   - RZ/G1E (R8A77450)