build(encrypt-fw): don't generate `build_msg.c`

This change avoids generating a build message source file on the shell,
instead using the `__DATE__` and `__TIME__` macros directly.

Change-Id: Ida537d4c3e550f2fbbd977472ed6573491d17c23
Signed-off-by: Chris Kay <chris.kay@arm.com>
3 files changed