BugLink: https://bugs.launchpad.net/bugs/1811646

Enable L1D flushing for AMD which was missed in the backport of
c595ceee ("x86/KVM/VMX: Add L1D flush logic").

Fixes: 57880666 ("x86/KVM/VMX: Add L1D flush logic")
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>