tools/testing/nvdimm: Add compile-test coverage for ndtest

Greg lamented:
"Ick, sorry about that, obviously this test isn't actually built by any
bots :("

A quick and dirty way to prevent this problem going forward is to always
compile ndtest.ko whenever nfit_test is built. While this still does not
expose the test code to any of the known build bots, it at least makes
it the case that anyone that runs the x86 tests also compiles the
powerpc test.

I.e. the Intel NVDIMM maintainers are less likely to fall into this hole
in the future.

Link: http://lore.kernel.org/r/2023112729-aids-drainable-5744@gregkh
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Yi Zhang <yi.zhang@redhat.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Link: https://lore.kernel.org/r/170191437889.426826.15528612879942432918.stgit@dwillia2-xfh.jf.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

tools/testing/nvdimm/test/Kbuild

@@ -7,6 +7,7 @@ obj-m += nfit_test_iomap.o
 
 ifeq  ($(CONFIG_ACPI_NFIT),m)
 	nfit_test-y := nfit.o
+	obj-m += ndtest.o
 else
 	nfit_test-y := ndtest.o
 endif