Use SPDX license identifiers ...

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>

Remove direct usage of __attribute__((foo)) ...

Migrate all direct usage of __attribute__ to usage of their
corresponding macros from cdefs.h.
e.g.:
 - __attribute__((unused)) -> __unused

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>

Make CASSERT() macro callable from anywhere ...

The CASSERT() macro introduces a typedef for the sole purpose of
triggering a compilation error if the condition to check is false.
This typedef is not used afterwards. As a consequence, when the
CASSERT() macro is called from withing a function block, the compiler
complains and outputs the following error message:

  error: typedef 'msg' locally defined but not used [-Werror=unused-local-typedefs]

This patch adds the "unused" attribute for the aforementioned
typedef. This silences the compiler warning and thus makes the
CASSERT() macro callable from within function blocks as well.

Change-Id: Ie36b58fcddae01a21584c48bb6ef43ec85590479

Separate out CASSERT macro into own header ...

Separate out the CASSERT macro out of bl_common.h into its own
header to allow more efficient header inclusion.

Change-Id: I291be0b6b8f9879645e839a8f0dd1ec9b3db9639