drm/i915: add fastboot param for fast & loose mode setting

Handling all the state properly for fastboot is still not yet done by
far, but we need some way to be able to test what we currently have.
So hide the not-yet-quite-complete stuff behind a module option.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
[danvet: Add a real commit message.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>