ARM: dts: at91: sama7g5: add node for the ADC

Add node for the ADC controller in sama7g5 SoC.

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20210901123013.329792-10-eugen.hristev@microchip.com