drm/i915: Give encoders useful names

Rather than let the core generate usless encoder names, let's pass in
something that actually identifies the piece of hardware we're dealing
with.

v2: Use 'DSI %c' instead of 'MIPI %c' for DSI encoders (Jani)
v3: Use port_name() in DSI code since we have it

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1464371966-15190-7-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index aa9c59e..096acbf0 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -5590,7 +5590,7 @@
 	encoder = &intel_encoder->base;
 
 	if (drm_encoder_init(dev, &intel_encoder->base, &intel_dp_enc_funcs,
-			     DRM_MODE_ENCODER_TMDS, NULL))
+			     DRM_MODE_ENCODER_TMDS, "DP %c", port_name(port)))
 		goto err_encoder_init;
 
 	intel_encoder->compute_config = intel_dp_compute_config;