drm/i915: Remove usage of encoder->new_crtc from clock computations

Some of the crtc_compute_clock() still depended on encoder->new_crtc
since they didn't use intel_pipe_will_have_type() and used an open
coded version of that function instead. This patch replaces those with
the appropriate code that checks the atomic state intead.

Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
[danvet: Separate the if (!connector) continue to facility easier
extraction of a loop iterator for all of these (there's lots more in
i915 and atomic helpers).]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>