drm/i915/dp: Boost timeout for enabling transcoder to 100ms

Adam Hill reported that his Arrandale system required a much longer, up
to 200x500us, wait for the panel to initialise or else modesetting would
fail.

References:

  https://bugs.freedesktop.org/show_bug.cgi?id=29141



Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reported-and-tested-by: Adam Hill <sidepipeuk@yahoo.co.uk>