Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/x86/lib/cpu.c b/arch/x86/lib/cpu.c
index 2dd1fe1..7ad6891 100644
--- a/arch/x86/lib/cpu.c
+++ b/arch/x86/lib/cpu.c
@@ -1,5 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include <linux/types.h>
 #include <linux/export.h>
+#include <asm/cpu.h>
 
 unsigned int x86_family(unsigned int sig)
 {