x86: ivybridge: Set up the LPC device using driver model

Find the LPC device in arch_cpu_init_dm() as a first step to converting
this code to use driver model. Probing the LPC will probe its parent (the
PCH) automatically, so make sure that probing the PCH does nothing before
relocation.

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