x86: add CPU field to struct thread_info

The CPU field will be moved back into thread_info even when
THREAD_INFO_IN_TASK is enabled, so add it back to x86's definition of
struct thread_info.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Borislav Petkov <bp@suse.de>
Acked-by: Mark Rutland <mark.rutland@arm.com>

arch/x86/include/asm/thread_info.h

@@ -57,6 +57,9 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	unsigned long		syscall_work;	/* SYSCALL_WORK_ flags */
 	u32			status;		/* thread synchronous flags */
+#ifdef CONFIG_SMP
+	u32			cpu;		/* current CPU */
+#endif
 };
 
 #define INIT_THREAD_INFO(tsk)			\