libnvdimm, dax: record the specified alignment of a dax-device instance

libnvdimm, dax: record the specified alignment of a dax-device instance

Orabug: 22913653

We want to use the alignment as the allocation and mapping unit.
Previously this information was only useful for establishing the data
offset, but now it is important to remember the granularity for the
later use.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Dan Duval <dan.duval@oracle.com>
(cherry picked from commit 45a0dac0451136fa7ae34a6fea53ef6a136287ce)

Conflicts:

	drivers/nvdimm/pfn.h
	drivers/nvdimm/pfn_devs.c