drm/i915: implement multifunction SDVO device support

With new intel_encoder/intel_connector structure change, each supported
connector type on SDVO device will be created as a new 'intel_connector',
and all attached to one 'intel_encoder' for its SDVO port.

The SDVO encoder will handle SDVO protocol stuff, and each connector does
its own part of work now, like detection is only to check if current active
output is itself, etc.

Update since last submit:
- Fixed SDVO TV property creation failure by incorrect set target output call

Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>