KVM: x86: Add support for save/load MSR_SMI_COUNT

KVM: x86: Add support for save/load MSR_SMI_COUNT

This MSR returns the number of #SMIs that occurred on
CPU since boot.

KVM commit 52797bf9a875 ("KVM: x86: Add emulation of MSR_SMI_COUNT")
introduced support for emulating this MSR.

This commit adds support for QEMU to save/load this
MSR for migration purposes.

Signed-off-by: Liran Alon <liran.alon@oracle.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>