Restructure kernel driver source tree

As a first step to have a clearer separation of the different parts of
the kernel driver, the source files have been placed into separate
directories according to their purpose and the different parts are only
allowed to use headers from another part in the include folder.

Files have been renamed accordingly to namespace them by their purpose.

Change-Id: I75e09ebf0002c99a22b6d4b09d34504d186c32b3
Signed-off-by: Mikael Olsson <mikael.olsson@arm.com>