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>

Previously, ZynqMP IPI in ATF is only for ZynqMP PM,
This patch is to have a ZynqMP IPI implementation to handle
both ZynqMP PM IPI requirement and IPI mailbox service requirement
which will be introduced next.

We control IPI agents registers access but not IPI buffers access in
this implementation. Each IPI mailbox user will directly access the
IPI buffers.

Signed-off-by: Wendy Liang <jliang@xilinx.com>