All identifiers, regardless of use, that start with two underscores are
reserved. This means they can't be used in header guards.

The style that this project is now to use the full name of the file in
capital letters followed by 'H'. For example, for a file called
"uart_example.h", the header guard is UART_EXAMPLE_H.

The exceptions are files that are imported from other projects:

- CryptoCell driver
- dt-bindings folders
- zlib headers

Change-Id: I50561bf6c88b491ec440d0c8385c74650f3c106e
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>

The H6 is Allwinner's most recent SoC. It shares most peripherals with the
other ARMv8 Allwinner SoCs (A64/H5), but has a completely different memory
map.

Introduce a separate platform target, which includes a different header
file to cater for the address differences. Also add the new build target
to the documentation.

The new ATF platform name is "sun50i_h6".

Signed-off-by: Andre Przywara <andre.przywara@arm.com>