x86: common thread_info definitions

Merge the thread_info definition into one structure definition for both arches.

The __u32 is equal to unsigned long for 32 bit.

sysenter_return is used both for the IA32 emulation for 64 and x86_32.
Avoid complicated #ifdef by simply always including it.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>