pmem: convert to generic memremap

pmem: convert to generic memremap

Orabug: 22913653

Kill arch_memremap_pmem() and just let the architecture specify the
flags to be passed to memremap().  Default to writethrough by default.

Suggested-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Dan Duval <dan.duval@oracle.com>
(cherry picked from commit e836a256e8fd579c9d7a3685f22981225a1ca451)

Conflict:

	include/linux/pmem.h