xen/pvh: Support ParaVirtualized Hardware extensions.

xen/pvh: Support ParaVirtualized Hardware extensions.

PVH allows PV linux guest to utilize hardware extended capabilities, such
as running MMU updates in a HVM container.

This patch allows it to be configured and enabled. Also, basic header file
changes to add new subcalls to physmap hypercall.

Lastly, mfn_to_local_pfn must return mfn for paging mode translate
(since we let the hypervisor - or CPU - do them for us).

Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Mukesh Rathor <mukesh.rathor@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>