libxc: make xc_memory_op library private

libxc: make xc_memory_op library private

Now that all XENMEM_* callers go via an op specific function make
xc_memory_op private to libxc (and rename to do_memory_op for
consistency with other private functions).

Also change the interface to take a size parameter so that
do_memory_op knows how much memory to lock for the top-level argument,
removing some of the introspection.

[ Compatibility note: this breaks qemu-xen before 706bc8c588cb ]

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