drm/i915: set the backlight panel delays registers to 1

Because we already do the wait in software: see
ironlake_wait_backlight_on and ironlake_edp_wait_backlight_off.

For the "backlight on" delay, even BSpec says we need to program 0x1
to PP_ON_DELAYS 12:0.

For the "backlight off" delay, if we don't do the same thing, when we
call ironlake_wait_panel_off we'll end up waiting for the it again.

On my machine the off delay is 200ms, so we save this amount of time
whenever we disable the panel (e.g, suspend).

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>