CVE-2017-5753
CVE-2017-5715

Set IBPB (Indirect branch prediction barrier) when switching VM.
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Andy Whitcroft <apw@canonical.com>
(backported from commit 472524f41206beb0a29c08f10689648a3dcd7707)
Signed-off-by: Andy Whitcroft <apw@canonical.com>