feat(debugv8p9): add support for FEAT_Debugv8p9

This patch enables FEAT_Debugv8p9 and prevents EL1/0 from
trapping to EL3 when accessing MDSELR_EL1 register by
setting the MDCR_EL3.EBWE bit.

Signed-off-by: Arvind Ram Prakash <arvind.ramprakash@arm.com>
Change-Id: I3613af1dd8cb8c0d3c33dc959f170846c0b9695a
diff --git a/changelog.yaml b/changelog.yaml
index 55fbba4..e4a6883 100644
--- a/changelog.yaml
+++ b/changelog.yaml
@@ -107,6 +107,9 @@
       - title: CPU feature / ID register handling in general
         scope: cpufeat
 
+      - title: Debug Extension (FEAT_Debugv8p9)
+        scope: debugv8p9
+
       - title: Guarded Control Stack (FEAT_GCS)
         scope: gcs