drm/i915: Don't pass dev_priv around so much

Simplify the calling convention of the skl+ watermark functions
by not passing around dev_priv needlessly. The callees have
what they need to dig it out anyway.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181114210729.16185-10-ville.syrjala@linux.intel.com


Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>