pmem: kill memremap_pmem()

pmem: kill memremap_pmem()

Orabug: 22913653

Now that the pmem-api is defined as "a set of apis that enables access
to WB mapped pmem",  the mapping type is implied.  Remove the wrapper
and push the functionality down into the pmem driver in preparation for
adding support for direct-mapped pmem.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
(cherry picked from commit a639315d6c536c806724c9328941a2517507e3e3)
Signed-off-by: Dan Duval <dan.duval@oracle.com>