drm/i915: Move load time PCH detect, DPIO, power domain SW init earlier

These are all SW only init steps not accessing the device and they only
need the platform identification macros to work, which are already
available earlier, so move these init steps earlier.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1458128348-15730-3-git-send-email-imre.deak@intel.com