x86: mp_init: Adjust bsp_init() to return more information

x86: mp_init: Adjust bsp_init() to return more information

This function is misnamed since it does not actually init the BSP. Also
it is convenient to adjust it to return a little more information.

Rename and update the function, to allow it to return the BSP CPU device
and number, as well as the total number of CPUs.

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>