drivers/nvdimm: Add nvdimm pmu structure

A structure is added called nvdimm_pmu, for performance
stats reporting support of nvdimm devices. It can be used to add
device pmu data such as pmu data structure for performance
stats, nvdimm device pointer along with cpumask attributes.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Nageswara R Sastry <rnsastry@linux.ibm.com>
Signed-off-by: Kajol Jain <kjain@linux.ibm.com>
Reviewed-by: Madhavan Srinivasan <maddy@in.ibm.com>
Link: https://lore.kernel.org/r/20220225143024.47947-2-kjain@linux.ibm.com


Signed-off-by: Dan Williams <dan.j.williams@intel.com>