cpu: change some globals to statics in drivers/base/cpu.c v2

This patch makes the following needlessly global code static:
- attr_online_map
- attr_possible_map
- attr_present_map

- cpu_state_attr [v2]

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Mike Travis <travis@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>