drm: Do not call drm_dp_cec_set_edid() while registering DP connectors

drm_dp_cec_register_connector() is called when registering each DP
connector in DRM, while sounds a good idea register CEC adapters as
earlier as possible, it causes some driver initialization delay
trying to do DPCD transactions in disconnected connectors.

This change will cause no regressions as drm_dp_cec_set_edid() will
still be called in further detection of connected connectors with a
valid edid parameter.

This change reduced the module load of i915 by average 0.5sec in a
machine with just one DP port disconnected while reducing more than
3sec in a machine with 4 DP ports disconnected.

Cc: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20181011004439.4482-1-jose.souza@intel.com