tmem: Batch and squash XEN_SYSCTL_TMEM_OP_SAVE_GET_POOL_[FLAGS,NPAGES,UUID]

tmem: Batch and squash XEN_SYSCTL_TMEM_OP_SAVE_GET_POOL_[FLAGS,NPAGES,UUID]
in one sub-call: XEN_SYSCTL_TMEM_OP_GET_POOLS.

These operations are used during the save process of migration.
Instead of doing 64 hypercalls lets do just one. We modify
the 'struct xen_tmem_client' structure (used in
XEN_SYSCTL_TMEM_OP_[GET|SET]_CLIENT_INFO) to have an extra field
'nr_pools'. Armed with that the code slurping up pages from the
hypervisor can allocate a big enough structure (struct tmem_pool_info)
to contain all the active pools. And then just iterate over each
one and save it in the stream.

We are also re-using one of the subcommands numbers for this,
as such the XEN_SYSCTL_INTERFACE_VERSION should be incremented
and that was done in the patch titled:
"tmem/libxc: Squash XEN_SYSCTL_TMEM_OP_[SET|SAVE].."

In the xc_tmem_[save|restore] we also added proper memory handling
of the 'buf' and 'pools'. Because of the loops and to make it as
easy as possible to review we add a goto label and for almost
all error conditions jump in it.

The include for inttypes is required for the PRId64 macro to
work (which is needed to compile this code under 32-bit).

Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>