ARM: dts: sun7i: Add Linutronix Testbox v2 board

The Testbox board is an open hardware enhancement for the Lamobo R1 router
board.  The Testbox board is used in the CI-RT project to manage devices
under test (https://ci-rt.linutronix.de).

The hardware project is located at https://github.com/ci-rt/testbox-shield



The Testbox v2 expands the Lamobo R1 router board with
- a power supply,
- a CAN bus PHY,
- a power control,
- a relay,
- an I2C EEPROM,
- a secure key storage (ATECC608a) and
- two RS232 compliant serial ports.

Co-developed-by: Benedikt Spranger <b.spranger@linutronix.de>
Signed-off-by: Benedikt Spranger <b.spranger@linutronix.de>
Signed-off-by: Bastian Germann <bage@linutronix.de>
[Maxime: Removed unused pinctrl node]
Signed-off-by: Maxime Ripard <maxime@cerno.tech>