mesa/st/glsl_to_tgsi: add class for array access tracking

mesa/st/glsl_to_tgsi: add class for array access tracking

Because of the indirect access it is impossible to obtain an accurate per
component and array element tracking. Therefore, the tracking is simplified
to only track whether any element was accessed, whether this happend
conditionally in a loop. In addition, while tracking of temporaries requires
a per-componet tracking that is later fused, for arrays only the components
access mask is neede. The resulting tracking code and evaluation of the array
live range is sufficiently different from the evaluation of the live range of
temporaries to justify implementing this in a different class instead of
adding more complexity to the already existing code for temporary life
range evaluation.

v4: Update commit message to make it clearer why this class is seperate from
    the tracking of temporaries.
Signed-off-by: Gert Wollny <gw.fossdev@gmail.com>
Acked-by: Dave Airlie <airlied@redhat.com>