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>
diff --git a/changelog.yaml b/changelog.yaml
index 4d84fb7..6a235cd 100644
--- a/changelog.yaml
+++ b/changelog.yaml
@@ -1416,6 +1416,9 @@
       - title: Certificate Creation Tool
         scope: cert-create
 
+      - title: Firmware Encryption Tool
+        scope: encrypt-fw
+
       - title: Memory Mapping Tool
         scope: memmap