Remove a duplicate definition of VP set (hv_vp_set) and use the common
definition (hv_vpset) that is used in other places.

Change the order of the members in struct hv_pcibus_device so that the
declaration of retarget_msi_interrupt_params is the last member. Struct
hv_vpset, which contains a flexible array, is nested two levels deep in
struct hv_pcibus_device via retarget_msi_interrupt_params.

Add a comment that retarget_msi_interrupt_params should be the last
member of struct hv_pcibus_device.
Signed-off-by: NMaya Nakamura <m.maya.nakamura@gmail.com>
Signed-off-by: NLorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: NMichael Kelley <mikelley@microsoft.com>
Reviewed-by: NVitaly Kuznetsov <vkuznets@redhat.com>
Tested-by: NVitaly Kuznetsov <vkuznets@redhat.com>