nvdimm: add missing MODULE_DESCRIPTION() macros

Fix the 'make W=1' warnings:
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/nvdimm/libnvdimm.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/nvdimm/nd_pmem.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/nvdimm/nd_btt.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/nvdimm/nd_e820.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/nvdimm/of_pmem.o
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/nvdimm/nd_virtio.o

[iweiny: edit core module description]

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Link: https://patch.msgid.link/r/20240526-md-drivers-nvdimm-v1-1-9e583677e80f@quicinc.com


Signed-off-by: Ira Weiny <ira.weiny@intel.com>