This is required to support keeping VCPU states across a system reset.
If we do not read the current state before the reset,
cpu_synchronize_all_post_reset may write back incorrect state
information.
The first user of this will be MCE MSR synchronization which currently
works around the missing cpu_synchronize_all_states.
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>