conf, qemu: move qemuDomainNVDimmAlignSizePseries to domain_conf.c

conf, qemu: move qemuDomainNVDimmAlignSizePseries to domain_conf.c

We'll use the auto-alignment function during parse time, in
domain_conf.c. Let's move the function to that file, renaming
it to virDomainNVDimmAlignSizePseries(). This will also make it
clearer that, although QEMU is the only driver that currently
supports it, pSeries NVDIMM restrictions aren't tied to QEMU.

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