hypervisor/xen/tools: Remove the XENMEM_get_oustanding_pages and provide the data...

hypervisor/xen/tools: Remove the XENMEM_get_oustanding_pages and provide the data via xc_phys_info

During the review of the patches it was noticed that there exists
a race wherein the 'free_memory' value consists of information from
two hypercalls. That is the XEN_SYSCTL_physinfo and XENMEM_get_outstanding_pages.

The free memory the host has available for guest is the difference between
the 'free_pages' (from XEN_SYSCTL_physinfo) and 'outstanding_pages'. As they
are two hypercalls many things can happen in between the execution of them.

This patch resolves this by eliminating the XENMEM_get_outstanding_pages
hypercall and providing the free_pages and outstanding_pages information
via the xc_phys_info structure.

It also removes the XSM hooks and adds locking as needed.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Reviewed-by: Tim Deegan <tim@xen.org>
Acked-by: Keir Fraser <keir.xen@gmail.com>