sunxi: Add defconfig for Sinlinx SinA31s

The Sinlinx A31s SDK is a A31s based module/baseboard development kit.

The core module has the SoC, PMIC, DRAM, eMMC and supporting components.
There are also pads for UART0, JTAG and I2S.

The baseboard has 100 Mbps Ethernet, 5x USB 2.0 host ports via a USB 2.0
hub chip, MMC, HDMI, SPDIF, CIR, audio jacks, 2 tablet-like volume
buttons, RS232 style UART and USB OTG (though VBUS is not connected).
Various headers are available for other addon modules, such as SDIO
WiFi, LCD display, camera sensor, UARTs, I2C, SPI and GPIOs.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>