drm/i915: s/vlv_num_wm_levels/intel_wm_num_levels/

Rename the VLV/CHV max_level->num_levels helper to have an intel_
prefix since it's not VLV/CHV specific and I'll want to use it on
other platforms as well.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170421181432.15216-4-ville.syrjala@linux.intel.com


Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>