pmem: convert to generic memremap

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>

diff --cc arch/x86/include/asm/io.h
Simple merge

diff --cc include/linux/pmem.h
Simple merge

diff --cc tools/testing/nvdimm/Kbuild
Simple merge

diff --cc tools/testing/nvdimm/test/iomap.c
Simple merge