ppc64 NVDIMM support was implemented in QEMU by commit [1].
The support is similar to what x86 already does, aside from
an extra 'uuid' element.

This patch introduces a new optional 'uuid' element for the
NVDIMM memory model. This element behaves like the 'uuid'
element of the domain definition - if absent, we'll create
a new one, otherwise use the one provided by the XML.
The 'uuid' element is exclusive to pseries guests and are
unavailable for other architectures.

Next patch will use this new element to add NVDIMM support
for ppc64.

[1] https://github.com/qemu/qemu/commit/ee3a71e36654317b14ede0290e87628f8b79f850Signed-off-by: NDaniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>