drm/i915: enable lvds pin pairs before dpll on gen2

Otherwise things migt not work too well.

Breakage introduced in

commit eb1cbe48
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Wed Mar 28 23:12:16 2012 +0200

    drm/i915: split PLL update code out of i9xx_crtc_mode_set

Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Cc: stable@vger.kernel.org (for 3.5 only)
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>