x86: Reduce back the alignment of the per-CPU data section

This complements commit:

  47f19a08: percpu: Remove the multi-page alignment facility

reverting one leftover of:

  fe8e0c25: x86, 32-bit: Align percpu area and irq stacks to THREAD_SIZE

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Acked-by: Alexander van Heukelum <heukelum@fastmail.fm>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <4D525CE60200007800030EE5@vpn.id2.novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Alexander van Heukelum <heukelum@fastmail.fm>