drm/i915/ddi: use struct for ddi buf translation tables

Try to avoid confusion with ARRAY_SIZE()/2 and hdmi_level*2.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
[danvet: Resolve silent patch conflict (didn't even fail to build)
with with Sonika's preceding patch to use the
hsw_ddi_translations_fdi table to driver the fdi link training
iteration loop. Also drop the double-write loop Damien spotted.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>