spi: ich: Move the protection/lockdown code into a function

spi: ich: Move the protection/lockdown code into a function

Reduce the size of the probe function but putting this code into its own
function.

Also remove the assumption that the PCH is always a parent of the SPI
controller, as this is not the case APL platforms. Use driver model to
find the PCH instead.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>