drm/i915/skl: AUX irqs have moved

Use the new AUX port irq bits where needed.

v2: Rebase on top of upstream changes
v3: Rebase on top of Oscar change to write IIR as soon as possible (Damien)
v4: Rebase on top of the for_each_pipe() change adding dev_priv as first
    argument (Damien)

Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>