libnvdimm, pmem: Change pmem physical sector size to PAGE_SIZE

Based on a patch: c8fa3173 brd: Request from fdisk 4k alignment by Boaz
Harrosh, allow fdisk to create properly aligned partitions for DAX. This
will also cause mkfs.ext4 to emit a warning if using a file system block
size of less than PAGE_SIZE.

Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Matthew Wilcox <matthew.r.wilcox@intel.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Elliott, Robert <Elliott@hp.com>
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
Acked-by: Boaz Harrosh <boaz@plexistor.com>
Acked-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>