Remove reference to pinmux group "wdt rst" on EW1200, ZBT-WG2626 and
ZBT-WG3526 devices. "wdt rst" is a pinmux function and not a pinmux
group.
Fixes the following error message during boot:
rt2880-pinmux pinctrl: invalid group "wdt rst" for function "gpio"
Signed-off-by: Kevin Darbyshire-Bryant <ldir@darbyshire-bryant.me.uk>