drm/i915: remove dev_priv->pc8.requirements_met

The requirements_met variable was used to track two things: enabled
CRTCs and the power well. After the latest chagnes, we get a runtime
PM reference whenever we get any of the power domains, and we get
power domains when we enable CRTCs or the power well, so we should
already be covered, not needing this specific tracking.

v2: - Rebase.
v3: - Rebase.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>