drm/i915: ddi: move pch setup after encoder->pre_enable

This is needed by an upcoming patch that moves the PCH/CRT PLL enabling
into the pre_enable hook, after which we want to keep the modeset
sequence at its current state. At this point this won't have an effect
since the PCH/CRT pre_enable hook is atm a NOP.

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