sunxi: add PineCube board

PineCube is an IP camera development kit released by Pine64.

It comes with the following compoents:

- A mainboard with Sochip S3 SoC, a 16MByte SPI Flash, AXP209 PMIC,
a power-only microUSB connector, a USB Type-A connector, a 10/100Mbps
Ethernet port and FPC connectors for camera and daughter board.
- An OV5640-based camera module which is connected to the parallel CSI
bus of the mainboard.
- A daughterboard with several buttons, a SD slot, some IR LEDs, a
microphone and a speaker connector.

As the device tree is synchronized in a previous commit, just add it to
Makefile, create a new MAINTAINER item and provide a defconfig.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
diff --git a/arch/arm/dts/Makefile b/arch/arm/dts/Makefile
index fd47e40..1a62e4c 100644
--- a/arch/arm/dts/Makefile
+++ b/arch/arm/dts/Makefile
@@ -590,6 +590,7 @@
 	sun8i-r40-bananapi-m2-ultra.dtb \
 	sun8i-v40-bananapi-m2-berry.dtb
 dtb-$(CONFIG_MACH_SUN8I_V3S) += \
+	sun8i-s3-pinecube.dtb \
 	sun8i-v3s-licheepi-zero.dtb
 dtb-$(CONFIG_MACH_SUN50I_H5) += \
 	sun50i-h5-bananapi-m2-plus.dtb \