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_fbc.c b/drivers/gpu/drm/i915/intel_fbc.c
index 5158500..c66ba7e 100644
--- a/drivers/gpu/drm/i915/intel_fbc.c
+++ b/drivers/gpu/drm/i915/intel_fbc.c
@@ -742,8 +742,7 @@ static void intel_fbc_update_state_cache(struct intel_crtc *crtc,
 
 	cache->crtc.mode_flags = crtc_state->base.adjusted_mode.flags;
 	if (IS_HASWELL(dev_priv) || IS_BROADWELL(dev_priv))
-		cache->crtc.hsw_bdw_pixel_rate =
-			ilk_pipe_pixel_rate(crtc_state);
+		cache->crtc.hsw_bdw_pixel_rate = crtc_state->pixel_rate;
 
 	cache->plane.rotation = plane_state->base.rotation;
 	cache->plane.src_w = drm_rect_width(&plane_state->base.src) >> 16;