libxc: wrappers for XENMEM {increase,decrease}_reservation and populate_physmap

libxc: wrappers for XENMEM {increase,decrease}_reservation and populate_physmap

Currently the wrappers for these hypercalls swallow partial success
and return failure to the caller.

In order to use these functions more widely instead of open-coding
uses of XENMEM_* and xc_memory_op add variants which return the actual
hypercall result.

Therefore add the following functions:
  xc_domain_increase_reservation
  xc_domain_decrease_reservation
  xc_domain_populate_physmap
and implement the existing semantics using these new functions as
  xc_domain_increase_reservation_exact
  xc_domain_decrease_reservation_exact
  xc_domain_populate_physmap_exact
replacing the existing xc_domain_memory_* functions.

Use these new functions to replace all open coded uses of
XENMEM_increase_reservation, XENMEM_decrease_reservation and
XENMEM_populate_physmap.

Also rename xc_domain_memory_*_pod_target to xc_domain_*_pod_target
for consistency.

Temporarily add a compatibility macro for
xc_domain_memory_populate_physmap to allow time for qemu to catch up.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>