Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
index eb5bbfe..8a0c25c 100644
--- a/arch/x86/include/asm/tsc.h
+++ b/arch/x86/include/asm/tsc.h
@@ -35,6 +35,7 @@
 
 extern void tsc_early_init(void);
 extern void tsc_init(void);
+extern unsigned long calibrate_delay_is_known(void);
 extern void mark_tsc_unstable(char *reason);
 extern int unsynchronized_tsc(void);
 extern int check_tsc_unstable(void);