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>

This function fills the buffer (first argument) with the specified
number of bytes (second argument) from the trusted entropy source.

This function will be used to initialize the stack protector canary.

Change-Id: Iff15aaf4778c13fa883ecb5528fcf9b8479d4489
Signed-off-by: dp-arm <dimitris.papastamos@arm.com>