It's only used in one function, and can be calculated without caching it
in the global struct by using drm_atomic_crtc_state_for_each_plane_state.

There are loops over all planes, including planes that don't exist.
This is harmless, because data_rate will always be 0 for them and we
never program them when updating watermarks.

Changes since v1:
- Rename rate back to data_rate, and change array name to
  plane_data_rate. (Matt)
- Remove whitespace. (Paulo)
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1477489299-25777-5-git-send-email-maarten.lankhorst@linux.intel.comReviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>