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>

At the moment we have two I2C stub drivers (for the Allwinner and the
Marvell platform), which #include the actual .c driver file.
Change this into the more usual design, by renaming and moving the stub
drivers into platform specific header files and including these from the
actual driver file. The platform specific include directories make sure
the driver picks up the right header automatically.

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