drm/i915: hsw: replace !is_pch_edp() with port==PORT_A

On HSW the CPU side eDP is always on port-A, the PCH side eDP is always
on port-D.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>