libnvdimm, pfn: add 'align' attribute, default to HPAGE_SIZE

libnvdimm, pfn: add 'align' attribute, default to HPAGE_SIZE

Orabug: 22913653

When setting aside capacity for struct page it must be aligned to the
largest mapping size that is to be made available via DAX.  Make the
alignment configurable to enable support for 1GiB page-size mappings.

The offset for PFN_MODE_RAM may now be larger than SZ_8K, so fixup the
offset check in nvdimm_namespace_attach_pfn().

Reported-by: Toshi Kani <toshi.kani@hpe.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
(cherry picked from commit 315c562536c42aa4da9b6c5a2135dd6715a5e0b5)
Signed-off-by: Dan Duval <dan.duval@oracle.com>