ARM: dts: rockchip: add recovery button for Rock2 Square

The recovery button is connected to ADC1.  This is the same setup as the
Firefly board, but for Rock2 the power supply is connected on the module
and all of the inputs are wired up to the edge connector, so use of the
ADC depends on the carrier board.

Signed-off-by: John Keeping <john@metanate.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>