tools/testing/nvdimm: Fix compilation failure without CONFIG_DEV_DAX_PMEM_COMPAT

When a kernel is configured without CONFIG_DEV_DAX_PMEM_COMPAT, the
compilation of tools/testing/nvdimm fails with:

Building modules, stage 2.
MODPOST 11 modules
ERROR: "dax_pmem_compat_test" [tools/testing/nvdimm/test/nfit_test.ko] undefined!

Fix the problem by calling dax_pmem_compat_test() only if the kernel has
the required functionality.

Signed-off-by: Jan Kara <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Dan Williams <[e-mail]>

tools/testing/nvdimm/test/nfit.c

···
 	mcsafe_test();
 	dax_pmem_test();
 	dax_pmem_core_test();
+#ifdef CONFIG_DEV_DAX_PMEM_COMPAT
 	dax_pmem_compat_test();
+#endif
 
 	nfit_test_setup(nfit_test_lookup, nfit_test_evaluate_dsm);