kernel/memremap, kasan: make ZONE_DEVICE with work with KASAN

KASAN learns about hotadded memory via the memory hotplug notifier.
devm_memremap_pages() intentionally skips calling memory hotplug
notifiers.  So KASAN doesn't know anything about new memory added by
devm_memremap_pages().  This causes a crash when KASAN tries to access
non-existent shadow memory:

 BUG: unable to handle kernel paging request at ffffed0078000000
 RIP: 0010:check_memory_region+0x82/0x1e0
 Call Trace:
  memcpy+0x1f/0x50
  pmem_do_bvec+0x163/0x720
  pmem_make_request+0x305/0xac0
  generic_make_request+0x54f/0xcf0
  submit_bio+0x9c/0x370
  submit_bh_wbc+0x4c7/0x700
  block_read_full_page+0x5ef/0x870
  do_read_cache_page+0x2b8/0xb30
  read_dev_sector+0xbd/0x3f0
  read_lba.isra.0+0x277/0x670
  efi_partition+0x41a/0x18f0
  check_partition+0x30d/0x5e9
  rescan_partitions+0x18c/0x840
  __blkdev_get+0x859/0x1060
  blkdev_get+0x23f/0x810
  __device_add_disk+0x9c8/0xde0
  pmem_attach_disk+0x9a8/0xf50
  nvdimm_bus_probe+0xf3/0x3c0
  drive...