drm/i915: Fix KMS regression on Sandybridge/CPT

We should enable FDI normal training on Sandybridge/CPT system
as well.

Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
[ickle: removed unrelated chunks]
Cc: stable@kernel.org
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>