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>

Currently the SCMI driver supports MHUv1, but Arm platforms may have
varied versions of MHU driver, with MHUv2 controllers being in the
latest Arm platforms.

This patch updates the SCMI driver to support MHUv2, specifically that
the sender must send the wake-up to the receiver before initiating any
data transfer.

Also, the existing mhu driver files, css_mhu.c and css_mhu.h, have been
moved from the scpi directory to a new directory, css/drivers/mhu.

Change-Id: I9b46b492a3e1d9e26db12d83a9773958a8c8402f
Signed-off-by: Samarth Parikh <samarth.parikh@arm.com>