drm/i915: Track MST link bandwidth

Use the added helpers to track MST link bandwidth for atomic modesets.
Link bw is acquired in the ->atomic_check() phase when CRTCs are being
enabled with drm_atomic_find_vcpi_slots(). Similarly, link bw is released
during ->atomic_check() with the connector helper callback ->atomic_check()
when CRTCs are disabled.

v6: active_changed does not alter vcpi allocations (Maarten)
v5: Implement connector->atomic_check() in place of atomic_release()
v4: Return an int from intel_dp_mst_atomic_release() (Maarten)
v3:
 Handled the case where ->atomic_release() is called more than once
 during an atomic_check() for the same state.
v2:
 Squashed atomic_release() implementation and caller (Daniel)
 Fixed logic for connector-crtc switching case (Daniel)
 Fixed logic for suspend-resume case.

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Archit Taneja <architt@codeaurora.org>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Harry Wentland <Harry.wentland@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1493421260-3146-1-git-send-email-dhinakaran.pandiyan@intel.com