drm/i915/psr: Extract PSR DPCD initialization and move it to intel_psr.c

intel_edp_init_dpcd() is cluttered with PSR specific DPCD checks and
intel_dp.c is huge.

No functional change intended.

v2: Rebased.

Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Reviewed-by: David Weinehall <david.weinehall@linux.intel.com>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180223221520.18464-3-dhinakaran.pandiyan@intel.com
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 95e2b69..e4b1e7d 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -1772,6 +1772,7 @@ static inline void intel_backlight_device_unregister(struct intel_connector *con
 
 /* intel_psr.c */
 #define CAN_PSR(dev_priv) (HAS_PSR(dev_priv) && dev_priv->psr.sink_support)
+void intel_psr_init_dpcd(struct intel_dp *intel_dp);
 void intel_psr_enable(struct intel_dp *intel_dp,
 		      const struct intel_crtc_state *crtc_state);
 void intel_psr_disable(struct intel_dp *intel_dp,