s390: 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 s390's definition of
struct thread_info.

Note that s390 always has CONFIG_SMP=y so there is no point in guarding
the CPU field with an #ifdef.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/include/asm/thread_info.h

@@ -37,6 +37,7 @@
 struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	unsigned long		syscall_work;	/* SYSCALL_WORK_ flags */
+	unsigned int		cpu;		/* current CPU */
 };
 
 /*