target-i386: move asm-x86/hyperv.h to standard-headers

The Hyper-V definitions are an industry standard and can be used
from code that is not KVM-specific.

Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>