ARM: dts: at91: Describe regulators on at91sam9g20ek

The at91sam9g20ek has no software controllable regulators, only some fixed
discrete regulators, but they are there and currently the wm8731 driver
does try to use them. Show the supplies in the DT and map them for the
wm8731 so things start up cleanly.

Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20220404102806.581374-3-broonie@kernel.org