KVM: selftests: define and use EVMCS_VERSION

KVM allows to use revision_id from MSR_IA32_VMX_BASIC as eVMCS revision_id
to workaround a bug in genuine Hyper-V (see the comment in
nested_vmx_handle_enlightened_vmptrld()), this shouldn't be used by
default. Switch to using KVM_EVMCS_VERSION(1).

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