libnvdimm/nfit_test: add firmware download emulation

Adding support in nfit_test for DSM v1.6 firmware update sequence. The test
will simulate the flashing of firmware to the DIMM. A bogus version string
will be returned as the test has no idea how to parse the firmware binary.
Any bogus binary can be used to "update" as the actual binary is not copied
into the kernel.

Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Reviewed-by: Vishal Verma <vishal.l.verma@intel.com>
[ vishal: also move smart calls into the nd_cmd_call block ]
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>