x86: ivybridge: Remove NORTHBRIDGE_INTEL_SANDYBRIDGE

NORTHBRIDGE_INTEL_SANDYBRIDGE is for sandybridge, not ivybridge.

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