drm/i915: get rid of dev_priv->info->has_pch_split

Previously we had has_pch_split to tell us whether we had a PCH or not
and we also had dev_priv->pch_type to tell us which kind of PCH it
was, but it could only be used if we were 100% sure we did have a PCH.
Now that PCH_NONE was added to dev_priv->pch_type we don't need
has_pch_split anymore: we can just check for pch_type != PCH_NONE.

The HAS_PCH_{IBX,CPT,LPT} macros use dev_priv->pch_type, so they can
only be called after intel_detect_pch. The HAS_PCH_SPLIT macro looks
at dev_priv->info->has_pch_split, which is available earlier.

Since the goal is to implement HAS_PCH_SPLIT using dev_priv->pch_type
instead of dev_priv->info->has_pch_split, we need to make sure that
intel_detect_pch is called before any calls to HAS_PCH_SPLIT are made.
So we moved the intel_detect_pch call to an earlier stage.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>