drivers/nvdimm: Add perf interface to expose nvdimm performance stats

drivers/nvdimm: Add perf interface to expose nvdimm performance stats

A common interface is added to get performance stats reporting
support for nvdimm devices. Added interface defines supported
event list, config fields for the event attributes and their
corresponding bit values which are exported via sysfs.

Interface also added support for pmu register/unregister functions,
cpu hotplug feature along with macros for handling events addition
via sysfs. It adds attribute groups for format, cpumask and events
to the pmu structure.

User could use the standard perf tool to access perf events exposed
via nvdimm pmu.

[Declare pmu functions in nd.h file to resolve implicit-function-declaration
warning and make hotplug function static as reported by kernel test robot]

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>
Link: https://lore.kernel.org/all/202202241242.zqzGkguy-lkp@intel.com/
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Madhavan Srinivasan <maddy@in.ibm.com>
Link: https://lore.kernel.org/r/20220225143024.47947-3-kjain@linux.ibm.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>