To make software license auditing simpler, use SPDX[0] license
identifiers instead of duplicating the license text in every file.

NOTE: Files that have been imported by FreeBSD have not been modified.

[0]: https://spdx.org/

Change-Id: I80a00e1f641b8cc075ca5a95b10607ed9ed8761a
Signed-off-by: dp-arm <dimitris.papastamos@arm.com>

Move the remaining IO storage source file (io_storage.c) from the
lib to the drivers directory. This requires that platform ports
explicitly add this file to the list of source files.

Also move the IO header files to a new sub-directory, include/io.

Change-Id: I862b1252a796b3bcac0d93e50b11e7fb2ded93d6