libxc: add p2m_size to xc_dom_image

libxc: add p2m_size to xc_dom_image

Add a new field p2m_size to keep track of the number of pages covered by
p2m.  Change total_pages to p2m_size in functions which in fact need
the size of p2m.

This is needed because we are going to ditch the assumption that PV x86
has only one contiguous ram region. Originally the p2m size was always
equal to total_pages, but we will soon change that in later patch.

This patch doesn't change the behaviour of libxc.

Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Dario Faggioli <dario.faggioli@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>