dt-bindings: watchdog: renesas,wdt: Add r9a09g011 (RZ/V2M) support

Add the documentation for the r9a09g011 SoC, but in doing so also
reorganise the doc to make it easier to read.
Additionally, make the binding require an interrupt to be specified.
Whilst the driver does not need an interrupt, all of the SoCs that use
this binding actually provide one.

Signed-off-by: Phil Edworthy <phil.edworthy@renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20220823093233.8577-2-phil.edworthy@renesas.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>