xen/changelog: Add SVE and "dom0" options to the changelog for Arm

Arm now can use the "dom0=" Xen command line option and the support
for guests running SVE instructions is added, put entries in the
changelog.

Mention the "Tech Preview" status and add an entry in SUPPORT.md

Signed-off-by: Luca Fancellu <luca.fancellu@arm.com>
Acked-by: Henry Wang <Henry.Wang@arm.com> # CHANGELOG
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>

CHANGELOG.md

@@ -11,6 +11,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
    cap toolstack provided values.
  - Ignore VCPUOP_set_singleshot_timer's VCPU_SSHOTTMR_future flag. The only
    known user doesn't use it properly, leading to in-guest breakage.
+ - The "dom0" option is now supported on Arm and "sve=" sub-option can be used
+   to enable dom0 guest to use SVE/SVE2 instructions.
 
 ### Added
  - On x86, support for features new in Intel Sapphire Rapids CPUs:
@@ -21,6 +23,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
      wide impact of a guest misusing atomic instructions.
  - xl/libxl can customize SMBIOS strings for HVM guests.
  - Add support for AVX512-FP16 on x86.
+ - On Arm, Xen supports guests running SVE/SVE2 instructions. (Tech Preview)
+
 
 ## [4.17.0](https://xenbits.xen.org/gitweb/?p=xen.git;a=shortlog;h=RELEASE-4.17.0) - 2022-12-12
 

SUPPORT.md

@@ -99,6 +99,12 @@ Extension to the GICv3 interrupt controller to support MSI.
 
     Status: Experimental
 
+### ARM Scalable Vector Extension (SVE/SVE2)
+
+Arm64 domains can use Scalable Vector Extension (SVE/SVE2).
+
+    Status: Tech Preview
+
 ## Guest Type
 
 ### x86/PV