Move chromebook_link over to driver model for PCI.

This involves:
- adding a uclass for platform controller hub
- removing most of the existing PCI driver
- adjusting how CPU init works to use driver model instead
- rename the lpc compatible string (it will be removed later)

This does not really take advantage of driver model fully, but it does work.
Furture work will improve the code structure to remove many of the explicit
calls to init the board.

Signed-off-by: Simon Glass <sjg@chromium.org>