sunxi: use sun6i-style watchdog for H6

The H6 SoC has a sun6i-style watchdog in its timer part.

Enable the usage of it.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>
Tested-by: Jagan Teki <jagan@amarulasolutions.com>