arm: add mach-nexell (header files)

Changes in relation to FriendlyARM's U-Boot nanopi2-v2016.01:
- DM_VIDEO support (display_dev.h).
- boot0.h added, handles NSIH --> tools/nexell obsolete.
- gpio.h: Include-path to errno.h changed.

Signed-off-by: Stefan Bosch <stefan_b@posteo.net>
12 files changed