x86: ivybridge: Move northbridge and PCH init into drivers

x86: ivybridge: Move northbridge and PCH init into drivers

Instead of calling the northbridge and PCH init from bd82x6x_init_extra()
when the PCI bus is probed, call it from the respective drivers. Also drop
the Northbridge init as it has no effect. The registers it touches appear to
be read-only.

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