arm64: dts: rockchip: Add saradc node to Indiedroid Nova

Add ADC support for the Indiedroid Nova, as well as the two ADC buttons
found on the device. The buttons are documented as "boot" and
"recovery". The boot button is used by the bootloader to boot into USB
recovery mode. The recovery button use is currently unknown.

Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Link: https://lore.kernel.org/r/20230918173255.1325-4-macroalpha82@gmail.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>