[POWERPC][XEN][LIBXC] Make xc_linux_build() use populate_physmap()

[POWERPC][XEN][LIBXC] Make xc_linux_build() use populate_physmap()
- populate_physmap() is the only way to invoke
  guest_physmap_{add/remove}_page(), which populate our new p2m table.
- To use it, we must to specify an array of PFNs where the new MFNs will be
  mapped.
- Split out alloc_memory() from xc_linux_build().
- Fix memory free path in xc_linux_build().
Signed-off-by: Ryan Harper <ryanh@us.ibm.com>
Signed-off-by: Hollis Blanchard <hollisb@us.ibm.com>
--HG--
extra : transplant_source : %9F%E6%FE%88%A6%A1%A2%88l%24%F2%AFvMf%3C%05%AF%DAU