x86: Move MP code into mp_init

At present the 'flight plan' for CPUs is passed into mp_init. But it is
always the same. Move it into the mp_init file so everything is in one
place. Also drop the SMI function since it does nothing. If we implement
SMIs, more refactoring will be needed anyway.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>