ARM64: hikey: hi6220: Add u-boot support for the 96boards CE HiKey board.

ARM64: hikey: hi6220: Add u-boot support for the 96boards CE HiKey board.

HiKey is the first 96boards consumer edition compliant board. It features a hi6220
SoC which has eight ARM A53 cpu's.

This initial port adds support for: -
1) Serial
2) eMMC / SD card
3) USB
4) GPIO

It has been tested with Arm Trusted Firmware running u-boot as the BL33 executable.

Notes:

eMMC has been tested with basic reading of eMMC partition into DDR. I have not
tested writing / erasing. Due to lack of clock control it won't be
running in the most performant high speed mode.

SD card slot has been tested for reading and booting kernels into DDR.
It is also currently configured to save the u-boot environment to the
SD card.

USB has been tested with ASIX networking adapter to tftpboot kernels
into DDR. On v2015.07-rc2 dhcp now works, and also USB mass storage
are correctly enumerated.

GPIO has been tested using gpio toggle GPIO4_1-3 to flash the LEDs.

Basic SoC datasheet can be found here: -
https://github.com/96boards/documentation/blob/master/hikey/
Hi6220V100_Multi-Mode_Application_Processor_Function_Description.pdf

Board schematic can be found here: -
https://github.com/96boards/documentation/blob/master/hikey/
96Boards-Hikey-Rev-A1.pdf

Signed-off-by: Peter Griffin <peter.griffin@linaro.org>