domain_conf.c: auto-align pSeries NVDIMM in virDomainMemoryDefPostParse()

domain_conf.c: auto-align pSeries NVDIMM in virDomainMemoryDefPostParse()

The alignment for the pSeries NVDIMM does not depend on runtime
constraints. This means that it can be done in device parse
time, instead of runtime, allowing the domain XML to reflect
what the auto-alignment would do when the domain starts.

This brings consistency between the NVDIMM size reported by the
domain XML and what the guest sees, without impacting existing
guests that are using an unaligned size - they'll work as usual,
but the domain XML will be updated with the actual size of the
NVDIMM.

Reviewed-by: Andrea Bolognani <abologna@redhat.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>