Merge miscellaneous libnvdimm updates for 4.21

* Use common helpers, bitmap_zalloc() and kstrndup(), to replace open
  coded versions.
* Clarify the comments around hotplug vs initial init case for the nfit
  driver.
* Cleanup the libnvdimm init path.

diff --cc drivers/acpi/nfit/core.c
Simple merge

diff --cc drivers/nvdimm/bus.c
Simple merge

diff --cc drivers/nvdimm/nd-core.h
Simple merge

diff --cc drivers/nvdimm/region_devs.c
Simple merge

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