CVE-2017-5753
CVE-2017-5715

Clear registers on VM exit to prevent speculative use of them.
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Andy Whitcroft <apw@canonical.com>
(cherry picked from commit fa3bf5051d2cb8df4c2ff38750c895ea497cc1d4)
Signed-off-by: Andy Whitcroft <apw@canonical.com>