A recent flurry of bug discoveries in the nfit driver's DSM marshalling routine has highlighted the fact that we do not have unit test coverage for this routine. Add a self-test of acpi_nfit_ctl() routine before probing the "nfit_test.0" device. This mocks stimulus to acpi_nfit_ctl() and if any of the tests fail "nfit_test.0" will be unavailable causing the rest of the tests to not run / fail. This unit test will also be a place to land reproductions of quirky BIOS behavior discovered in the field and ensure the kernel does not regress against implementations it has seen in practice. Signed-off-by: Dan Williams <dan.j.williams@intel.com>