We were apparently relying on the defaults on BDW, which resulted in no
hotplug or AUX interrupts.  So be sure to call the ibx_irq_preinstall to
enable all interrupts.

v2: use preinstall instead of redundant SDIER write

References: https://bugs.freedesktop.org/show_bug.cgi?id=72834
References: https://bugs.freedesktop.org/show_bug.cgi?id=72833


Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>