x86: ivybridge: Convert enable_usb_bar() to use DM PCI API

Convert this function over to use the driver model PCI API. In this case
we want to avoid using the real PCI devices since they have not yet been
probed. Instead, write directly to their PCI configuration address.

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