drm/i915: fix sdvo hotplug support check and activation

The sdvo hotplug support check and activation has worked by coincidence for
TMDS0. The boolean value returned by intel_sdvo_supports_hotplug() was
masked with a bit shifted by device number, which also should have been one
of SDVO_OUTPUT_* bits instead. Boolean true masked with 1 shifted by 0 just
happened to match SDVO_OUTPUT_TMDS0...

Get hotplug support as a bit mask, check the correct bits for support, and
use the correct bits for activating hotplug support.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Simon Farnsworth <simon.farnsworth@onelan.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>