drm/i915: Split out runtime configuration of device info to its own file

Let's reclaim a few hundred lines from i915_drv.c by splitting out the
runtime configuration of the "constant" dev_priv->info.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1467711623-2905-1-git-send-email-chris@chris-wilson.co.uk


Reviewed-by: Matthew Auld <matthew.auld@intel.com>