drm/i915: Use a dmi quirk to skip a broken SDVO TV output.

This IBM system has a multi-function SDVO card that reports both VGA
and TV, but the system has no TV connector.  The TV connector always
reported as connected, which would lead to poor modesetting choices.

https://bugs.freedesktop.org/show_bug.cgi?id=25787

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Tested-by: Vance <liangghv@sg.ibm.com>
Cc: stable@kernel.org
Signed-off-by: Eric Anholt <eric@anholt.net>