dt-bindings: reset: renesas,rst: Document R-Car V4M support

Document support for the Reset (RST) module in the Renesas R-Car V4M
(R8A779H0) SoC.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Link: https://lore.kernel.org/r/bd26299d687412c20fea5e2d57195a763cc532e9.1706194617.git.geert+renesas@glider.be