drm/i915: power domains: add vlv power wells

drm/i915: power domains: add vlv power wells

Based on an early draft from Jesse.

Add support for powering on/off the dynamic power wells on VLV by
registering its display and dpio dynamic power wells with the power
domain framework.

For now power on all PHY TX lanes regardless of the actual lane
configuration. Later this can be optimized when the PHY side setup
enables only the required lanes. Atm, it enables all lanes in all
cases.

v2:
- undef function local COND macro after its last use (Ville)
- Take dev_priv->irq_lock around the whole sequence of
  intel_set_cpu_fifo_underrun_reporting_nolock() and
  valleyview_disable_display_irqs(). They are short and releasing
  the lock in between only makes proving correctness more difficult.
- sanitize local var names in vlv_power_well_enabled()
v3:
- rebase on latest -nightly

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
[danvet: Resolve conflict due to my changes in the previous patch.
Also throw in an assert_spin_locked for safety. And finally appease
checkpatch.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>