drm/i915: read out hw state earlier v2

We want to do this early on before we try to fetch the plane config,
which depends on some of the pipe config state.

Note that the important part is that we do this before we initialize
gem, since otherwise we can't properly pre-reserve the stolen memory
for framebuffers inherited from the bios.

v2: split back out from get_plane_config change (Daniel)
    update for recent locking & reset changes (Jesse)

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
[danvet: Explain a bit more why we need to move this.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>