KVM: hyperv: define VP assist page helpers

[ Upstream commit 72bbf9358c3676bd89dc4bd8fb0b1f2a11c288fc ]

The state related to the VP assist page is still managed by the LAPIC
code in the pv_eoi field.

Signed-off-by: Ladi Prosek <lprosek@redhat.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>