libnvdimm for v5.15

- Fix a race condition in the teardown path of raw mode pmem namespaces.

- Cleanup the code that filesystems use to detect filesystem-dax
  capabilities of their underlying block device.
Merge branch 'for-5.15/fsdax-cleanups' into for-5.15/libnvdimm

Include Christoph's rework of the dax_supported() helpers in the v5.15
libnvdimm update. This supports the ongoing dax-reflink enabling effort.