x86: cpu/common.c cleanups

- fix various style problems
 - declare varibles before they get used
 - introduced clear_all_debug_regs
 - fix header files issues

LKML-Reference: <1237009789.4387.2.camel@localhost.localdomain>
Signed-off-by: Jaswinder Singh Rajput <jaswinder@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>