build(rzg-layout): split combined targets

This is a small change to split up the generation of the RZ/G layout
images into unique targets. This is predominantly for cleanliness
reasons - Make current doesn't know about the `.bin` and `.srec`
binaries generated by the `.elf` target.

Change-Id: I81251ac647b85c5eec8f910ddc841a5a32b49e67
Signed-off-by: Chris Kay <chris.kay@arm.com>
diff --git a/changelog.yaml b/changelog.yaml
index 302546e..55fbba4 100644
--- a/changelog.yaml
+++ b/changelog.yaml
@@ -1434,6 +1434,10 @@
         subsections:
           - title: R-Car Layout Tool
             scope: rcar-layout
+
+          - title: R/ZG Layout Tool
+            scope: rzg-layout
+
   - title: Dependencies
     scope: deps