libnvdimm, pfn: 'struct page' provider infrastructure

libnvdimm, pfn: 'struct page' provider infrastructure

Orabug: 22913653

Implement the base infrastructure for libnvdimm PFN devices. Similar to
BTT devices they take a namespace as a backing device and layer
functionality on top. In this case the functionality is reserving space
for an array of 'struct page' entries to be handed out through
pfn_to_page(). For now this is just the basic libnvdimm-device-model for
configuring the base PFN device.

As the namespace claiming mechanism for PFN devices is mostly identical
to BTT devices drivers/nvdimm/claim.c is created to house the common
bits.

Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
(cherry picked from commit e1455744b27c9e6115c3508a7b2902157c2c4347)
Signed-off-by: Dan Duval <dan.duval@oracle.com>