drm/i915: s/vlv_plane_wm_compute/vlv_raw_plane_wm_compute/ etc.

Rename some of the vlv wm functions to reflect the fact that they
operate on the "raw" watermarks.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170421181432.15216-2-ville.syrjala@linux.intel.com


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