Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/x86/boot/string.h b/arch/x86/boot/string.h
index 3d78e27..38d8f2f 100644
--- a/arch/x86/boot/string.h
+++ b/arch/x86/boot/string.h
@@ -29,4 +29,5 @@
 extern unsigned long long simple_strtoull(const char *cp, char **endp,
 					  unsigned int base);
 
+int kstrtoull(const char *s, unsigned int base, unsigned long long *res);
 #endif /* BOOT_STRING_H */