sunxi: Enable SPL support for A80 Optimus board

The A80 Optimus Board was launched with the Allwinner A80 SoC.
It was jointly developed by Allwinner and Merrii.

This board has a UART port, a JTAG connector, 2 USB host ports, a USB
3.0 OTG connector, an HDMI output, a micro SD slot, 16G eMMC flash,
2G DRAM, a camera sensor interface, a WiFi/BT combo chip, a headphone
jack, IR receiver, and additional GPIO headers.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
[hdegoede@redhat.com: update existing Merrii_A80_Optimus_defconfig
 instead of adding a new defconfig]
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>