ARM: dts: at91: remove deprecated ADC properties

atmel,adc-res, atmel,adc-res-names and the trigger nodes are not parsed by
the driver anymore and the information is now defined in the driver data.

Also remove the leftover #address-cells and #size-cells that were used when
the trigger nodes had a unit-address.

Finally, the default is already to use the highest resoution. Remove
atmel,adc-use-res from the SoC dtsi.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Reviewed-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Link: https://lore.kernel.org/r/20201128222818.1910764-11-alexandre.belloni@bootlin.com