drm/i915: Populate pipe_offsets[] & co. accurately

At some point people have started to assume that
pipe_offsets[] & co. are only populated for pipes and whatnot
that actually exist. That is in fact not currently true, but
we can easily make it so.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190305192905.7140-1-ville.syrjala@linux.intel.com


Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>