Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/ia64/include/asm/sal.h b/arch/ia64/include/asm/sal.h
index 588f331..08f5b6a 100644
--- a/arch/ia64/include/asm/sal.h
+++ b/arch/ia64/include/asm/sal.h
@@ -43,6 +43,7 @@
 #include <asm/pal.h>
 #include <asm/fpu.h>
 
+extern unsigned long sal_systab_phys;
 extern spinlock_t sal_lock;
 
 /* SAL spec _requires_ eight args for each call. */