drm/i915: Add connector dbgfs for all connectors

Add connector debugfs attributes for each intel
connector which is getting register.

v2:
- adding connector debugfs for each connector in
  intel_connector_register() to fix CI failure for legacy connectors.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200415170555.15531-4-anshuman.gupta@intel.com