tools/testing/nvdimm: add mock acpi_nfit_flush_address entries to nfit_test

In preparation for fixing the BLK path to properly use "directed
pcommit" enable the unit test infrastructure to emit mock "flush"
tables.  Writes to these flush addresses trigger a memory controller to
flush its internal buffers to persistent media, similar to the x86
"pcommit" instruction.

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