pvh dom0: memory leak from iomem map

[Mukesh Rathor <mukesh.rathor@oracle.com>]

Hi Tim,

When building a dom0 pvh, we populate the p2m with 0..N pfns upfront. Then
in pvh_map_all_iomem, we walk the e820 and map all iomem 1:1. As such
any iomem range below N would cause those ram frames to be silently dropped. 
Since the holes could be pretty big, I am concenred this could result
in significant loss of frames. 

In my very early patches I had:

set_typed_p2m_entry():
...
    else if ( p2m_is_ram(ot) )
    {
         if ( is_pvh_domain(d) )                    <---
             free_domheap_page(mfn_to_page(omfn));  <---

         ASSERT(mfn_valid(omfn));
         set_gpfn_from_mfn(mfn_x(omfn), INVALID_M2P_ENTRY);
..

I'd like you to reconsider it. Since there is a dislike using is_pvh, 
I suppose one alternative could be, 'if ( gfn_p2mt == p2m_mmio_direct)'.

If you have any other suggestions, I'm open to them. LMK your thoughts..

Thanks,
Mukesh