x86_32: use generic percpu.h

x86_32 only provides a special way to obtain the local per cpu area offset
via x86_read_percpu. Otherwise it can fully use the generic handling.

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