drm/i915: fix PCH_NOP setting for non-PCH platforms

drm/i915: fix PCH_NOP setting for non-PCH platforms

Setting PCH type to PCH_NOP before checking whether we actually have a
PCH ends up returning true for HAS_PCH_SPLIT() on all non-PCH split
platforms. Fix this by using PCH_NOP only for platforms that actually
have a PCH.

Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180608123330.31003-6-jani.nikula@intel.com