drm/i915: Check of !HAS_PCH_SPLIT() in PCH transcoder funcs

Check for !HAS_PCH_SPLIT() instead of 'gen < 5' in the PCH transcoder
enable functions.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>