drm/i915: Use ilk_wm_max_level() in latency debugfs files

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
[danvet: Squash in patch that exported ilk_wm_max_level.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --cc drivers/gpu/drm/i915/i915_debugfs.c
Simple merge

diff --cc drivers/gpu/drm/i915/intel_drv.h
Simple merge

diff --cc drivers/gpu/drm/i915/intel_pm.c
Simple merge