drm/i915: Store the pipe pixel rate in the crtc state

Rather than recomputing the pipe pixel rate on demand everywhere, let's
just stick the precomputed value into the crtc state.

v2: Rebase due to min_pixclk[] code movement
    Document the new pixel_rate struct member (Ander)
    Combine vlv/chv with bdw+ in intel_modeset_readout_hw_state()
v3: Fix typos in commit message (David)

Cc: Ander Conselvan De Oliveira <conselvan2@gmail.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170126195031.32343-1-ville.syrjala@linux.intel.com
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 973d7b6..e1dbd9a 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -544,6 +544,12 @@ struct intel_crtc_state {
 	 * and get clipped at the edges. */
 	int pipe_src_w, pipe_src_h;
 
+	/*
+	 * Pipe pixel rate, adjusted for
+	 * panel fitter/pipe scaler downscaling.
+	 */
+	unsigned int pixel_rate;
+
 	/* Whether to set up the PCH/FDI. Note that we never allow sharing
 	 * between pch encoders and cpu encoders. */
 	bool has_pch_encoder;