pc: drop memory region alignment check for 0

All applicable memory regions always have an alignment > 0. All memory
backends result in file_ram_alloc() or qemu_anon_ram_alloc() getting
called, setting the alignment to > 0.

So a PCDIMM memory region always has an alignment > 0. NVDIMM copy the
alignment of the original memory memory region into the handcrafted memory
region that will be used at this place.

So the check for 0 can be dropped and we can reduce the special
handling.

Dropping this check makes factoring out of alignment handling easier as
compat handling only has to look at pcmc->enforce_aligned_dimm and not
care about the alignment of the memory region.

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20180801133444.11269-4-david@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>