arm64: dts: allwinner: a64: add support for PineTab

PineTab is a 10.1" tablet by Pine64 with Allwinner A64 inside.

It includes the following peripherals:

USB:
- A microUSB Type-B port connected to the OTG-capable USB PHY of
Allwinner A64. The ID pin is connected to a GPIO of the A64 SoC, and the
Vbus is connected to the Vbus of AXP803 PMIC. These enables OTG
functionality on this port.
- A USB Type-A port is connected to the internal hub attached to the
non-OTG USB PHY of Allwinner A64.
- There are reserved pins for an external keyboard connected to the
internal hub.

Power:
- The microUSB port has its Vbus connected to AXP803, mentioned above.
- A DC jack (of a strange size, 2.5mm outer diameter) is connected to
the ACIN of AXP803.
- A Li-Polymer battery is connected to the battery pins of AXP803.

Storage:
- An tradition Pine64 eMMC slot is on the board, mounted with an eMMC
module by factory.
- An external microSD slot is hidden under a protect case.

Display:
- A MIPI-DSI LCD panel (800x1280) is connected to the DSI port of A64 SoC.
- A mini HDMI port.

Input:
- A touch panel attached to a Goodix GT9271 touch controller.
- Volume keys connected to the LRADC of the A64 SoC.

Camera:
- An OV5640 CMOS camera is at rear, connected to the CSI bus of A64 SoC.
- A GC2145 CMOS camera is at front, shares the same CSI bus with OV5640.

Audio:
- A headphone jack is conencted to the SoC's internal codec.
- A speaker connected is to the Line Out port of SoC's internal codec, via
an amplifier.

Misc:
- Debug UART is muxed with the headphone jack, with the switch next to
the microSD slot.
- A bosch BMA223 accelerometer is connected to the I2C bus of A64 SoC.
- Wi-Fi and Bluetooth are available via a RTL8723CS chip, similar to the
one in Pinebook.

This commit adds a basically usable device tree for it, implementing
most of the features mentioned above. HDMI is not supported now because
bad LCD-HDMI coexistence situation of mainline A64 display driver, the
front camera currently lacks a driver and a facility to share the bus
with the rear one, and the accelerometer currently lacks a DT binding.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>