feat(neoverse-rd): add scope for SGI-575

As SGI-575 would need a dedicated scope for use, define the scope
'sgi575' under the subsection within Neoverse-RD platforms.

Change-Id: I872dc3bceace5c3358cde24fff1c4c17207ec962
Signed-off-by: Rohit Mathew <rohit.mathew@arm.com>
diff --git a/changelog.yaml b/changelog.yaml
index 134e72d..3469cc5 100644
--- a/changelog.yaml
+++ b/changelog.yaml
@@ -219,6 +219,9 @@
             scope: neoverse-rd
 
             subsections:
+              - title: SGI-575
+                scope: sgi575
+
               - title: RD-N1 Edge
                 scope: rdn1edge