dax: update I/O path to do proper PMEM flushing

dax: update I/O path to do proper PMEM flushing

Orabug: 22913653

Update the DAX I/O path so that all operations that store data (I/O
writes, zeroing blocks, punching holes, etc.) properly synchronize the
stores to media using the PMEM API.  This ensures that the data DAX is
writing is durable on media before the operation completes.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
(cherry picked from commit 2765cfbb342c727c3fd47b165196cb16da158022)
Signed-off-by: Dan Duval <dan.duval@oracle.com>