x86: change thread_info's flag field back to 32 bits

Impact: pack struct thread_info more tightly

Change x86_64's thread_info 'flags' field back to __u32.

This was changed to 'unsigned long' when the thread_info*.h
for i386 and x86_64 were merged.  Change it back.  We can
do this as only 27 bits of 'flags' are actually used.

This change actually packs down thread_info by 64 bits:
32 bits are saved by the smaller flags, and 32 bits are
saved by the following 'mm_segment_t field' becoming
naturally 64-bit aligned.
Signed-off-by: Joe Korty <joe.korty@ccur.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/include/asm/thread_info.h

@@ -24,7 +24,7 @@ struct exec_domain;
 struct thread_info {
 	struct task_struct	*task;		/* main task structure */
 	struct exec_domain	*exec_domain;	/* execution domain */
-	unsigned long		flags;		/* low level flags */
+	__u32			flags;		/* low level flags */
 	__u32			status;		/* thread synchronous flags */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable,