x86: add stringify header

We use a __stringify construction at paravirt_patch_64.c.
It's better practice to include the stringify header directly

Signed-off-by: Glauber de Oliveira Costa <gcosta@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/paravirt_patch_64.c

@@ -1,5 +1,6 @@
 #include <asm/paravirt.h>
 #include <asm/asm-offsets.h>
+#include <linux/stringify.h>
 
 DEF_NATIVE(pv_irq_ops, irq_disable, "cli");
 DEF_NATIVE(pv_irq_ops, irq_enable, "sti");