x86: ivybridge: Convert SDRAM init to use driver model

x86: ivybridge: Convert SDRAM init to use driver model

SDRAM init needs access to the Northbridge controller and the Intel
Management Engine device. Add the latter to the device tree and convert all
of this code to driver model.

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