x86: apl: Hide the p2sb on exit from U-Boot

This confuses Linux's PCI probing so needs to be hidden when booting
Linux. Add a remove() method to handle this.

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