drm/i915: Add 30ms delay to make SDVO TV detection reliable.

Without this, on some boots the TV wouldn't be detected.  Testing
showed 15ms to be insufficient.

https://bugs.freedesktop.org/show_bug.cgi?id=24290
https://bugs.freedesktop.org/show_bug.cgi?id=20785



Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Tested-by: Yan Seiner <yan@seiner.com>
Signed-off-by: Eric Anholt <eric@anholt.net>