changelog: note MSR access change

The change to deny all accesses to MSRs indexes not explicitly handled
prevents leaking unwanted data into guests.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Release-Acked-by: Ian Jackson <iwj@xenproject.org>

CHANGELOG.md

@@ -12,6 +12,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
  - ARM IOREQ servers (device emulation etc.) (Tech Preview)
  - Renesas IPMMU-VMSA (Supported, not security supported; was Tech Preview)
  - ARM SMMUv3 (Tech Preview)
+ - Switched MSR accesses to deny by default policy.
 
 ## Removed / support downgraded