Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/csky/Kconfig.debug b/arch/csky/Kconfig.debug
new file mode 100644
index 0000000..295942f
--- /dev/null
+++ b/arch/csky/Kconfig.debug
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+# dummy file, do not delete