x86/Hyper-V: Fix definition of struct hv_vp_assist_page

The struct hv_vp_assist_page was defined incorrectly.
The "vtl_control" should be u64[3], "nested_enlightenments
_control" should be a u64 and there are 7 reserved bytes
following "enlighten_vmentry". Fix the definition.

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