x86: mp_init: Avoid declarations in header files

The functions used by the flight plan are declared in the header file but
are not used in any other file.

Move the flight plan steps down to just above where it is used so that we
can make these function static.

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>