x86: cpu/common*.c have same cpu_init(), with copying and #ifdef

hard to merge by lines... (as here we have material differences between
32-bit and 64-bit mode) - will try to do it later.

Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>