arm64: dts: allwinner: Add initial support for Pine64 PinePhone

At the moment PinePhone comes in two slightly incompatible variants:

- 1.0: Early Developer Batch
- 1.1: Braveheart Batch

There will be at least one more incompatible variant in the very near
future, so let's start by sharing the dtsi among multiple variants,
right away, even though the HW description doesn't yet include the
different bits.

The differences between 1.0 and 1.1 are: change in pins that control
the flash LED, differences in modem power status signal routing, and
maybe some other subtler things, that have not been determined yet.

This is a basic DT that includes only features that are already
supported by mainline drivers.

Co-developed-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Samuel Holland <samuel@sholland.org>
Co-developed-by: Martijn Braam <martijn@brixit.nl>
Signed-off-by: Martijn Braam <martijn@brixit.nl>
Co-developed-by: Luca Weiss <luca@z3ntu.xyz>
Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
Signed-off-by: Bhushan Shah <bshah@kde.org>
Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Ondrej Jirman <megous@megous.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>