KVM: x86: do not save guest-unsupported XSAVE state

KVM: x86: do not save guest-unsupported XSAVE state

commit 00c87e9a70a17b355b81c36adedf05e84f54e10d upstream.

Saving unsupported state prevents migration when the new host does not
support a XSAVE feature of the original host, even if the feature is not
exposed to the guest.

We've masked host features with guest-visible features before, with
4344ee981e21 ("KVM: x86: only copy XSAVE state for the supported
features") and dropped it when implementing XSAVES.  Do it again.

Fixes: df1daba7d1cb ("KVM: x86: support XSAVES usage in the host")
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>