sun6i: Add new board Merrii Hummingbird A31

The Merrii Hummingbird A31 is a A31 based development board with 1G
RAM, 8G NAND, AP6210 WiFi+BT, gigabit ethernet, USB OTG, 2 USB 2.0
ports connected to a USB hub chip, HDMI, VGA, TV and stereo in/out.

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>
sunxi: Align PSCI stack calculation to comment

0x400 is true 1K.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Ian Campbell <ijc@hellion.org.uk>