dm: Expand the uclass for Platform Controller Hubs (PCH)

dm: Expand the uclass for Platform Controller Hubs (PCH)

A Platform Controller Hub is an Intel concept - it is like the peripherals
on an SoC and is often in a separate chip from the CPU. The chip is typically
found on the first PCI bus and integrates multiple devices.

We have a very simple uclass to support PCHs. Add a few operations, such as
setting up the devices on the PCH and finding the SPI controller base
address. Also move it into drivers/pch/ since we will be adding a few PCH
drivers.

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