arm64: dts: rockchip: rk3328: Add Radxa ROCK Pi E

Radxa ROCK Pi E is a router oriented SBC based on Rockchip's RK3328 SoC.
As the official wiki page puts it, "E for Ethernets".

It features the RK3328 SoC, gigabit and fast Ethernet RJ45 ports, both
directly served by Ethernet controllers in the SoC, a USB 3.0 host port,
a power-only USB type-C port, a 3.5mm headphone jack for audio output,
two LEDs, a 40-pin Raspberry Pi style GPIO header, and optional WiFi+BT
and PoE header.

The board comes in multiple configurations, differing in the amount of
onboard RAM, the level of WiFi+BT (none, 802.11n 2.4GHz, or 802.11ac
2.4 GHz & 5 GHz), and whether PoE is supported or not. These variants
can all share the same device tree.

The USB 2.0 OTG controller is available on the 40-pin header. This is
not enabled in the device tree, since it is possible to use it in a
host-only configuration, or in OTG mode with an extra pin from the
header as the ID pin.

The device tree is based on the one of the Rock64, with various parts
modified to match the ROCK Pi E, and some parts updated to newer styles,
such as the gmac2io node's mdio sub-node.

Add a new device tree file for the new board.

The voltages for the adc-keys were selected to have some tolerances for
resistor variances and the ADC itself also causing voltage drops. Since
the recover button is the only button on the adc line, this should not
cause any issues.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Link: https://lore.kernel.org/r/20210117100710.4857-4-wens@kernel.org
Signed-off-by: Heiko Stuebner <heiko@sntech.de>