Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/tools/testing/nvdimm/watermark.h b/tools/testing/nvdimm/watermark.h
index ed05287..43fc4f3 100644
--- a/tools/testing/nvdimm/watermark.h
+++ b/tools/testing/nvdimm/watermark.h
@@ -6,6 +6,9 @@
 int libnvdimm_test(void);
 int acpi_nfit_test(void);
 int device_dax_test(void);
+int dax_pmem_test(void);
+int dax_pmem_core_test(void);
+int dax_pmem_compat_test(void);
 
 /*
  * dummy routine for nfit_test to validate it is linking to the properly