util/broadcom/secimage: Add HMAC test

One of responsibilities of the `secimage` tool is signing the image
using the HMAC-SHA256 algorithm. The test being added verifies that
secimage's internal call yields same result as the according openssl
tool does.

Change-Id: I8de4328f435af56901a861e3d5e733657c3c7f78
Signed-off-by: Alex Thiessen <alex.thiessen.de+coreboot@gmail.com>
Reviewed-on: https://review.coreboot.org/23474
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
7 files changed