drm/i915: Add state readout and checking for has_dp_encoder and dp_m_n

Add functions to read out the CPU and PCH transcoder M/N values,
and use them to fill out the pipe config dp_m_n information. And
while at it populate has_dp_encoder too.

Also refactor ironlake_get_fdi_m_n_config() to simply call the new
intel_cpu_transcoder_get_m_n() function.

v2: Remember the DDI

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index b6393e2..f6d5c92 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -801,5 +801,7 @@
 extern void hsw_pc8_restore_interrupts(struct drm_device *dev);
 extern void intel_aux_display_runtime_get(struct drm_i915_private *dev_priv);
 extern void intel_aux_display_runtime_put(struct drm_i915_private *dev_priv);
+extern void intel_dp_get_m_n(struct intel_crtc *crtc,
+			     struct intel_crtc_config *pipe_config);
 
 #endif /* __INTEL_DRV_H__ */