selftests: kvm: fix state save/load on processors without XSAVE

state_test and smm_test are failing on older processors that do not
have xcr0.  This is because on those processor KVM does provide
support for KVM_GET/SET_XSAVE (to avoid having to rely on the older
KVM_GET/SET_FPU) but not for KVM_GET/SET_XCRS.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>