This adds initial support for the A64 Allwinner SoC to LEDE.
It will be build in the new cortexa53 subtarget.

Currently it only supports the pine64 and the image is able to boot on
this SoC.

Camera, Ethernet, HDMI and other parts are currently not working.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>