st/nine: Rewrite LOOP implementation, and a0 aL handling

st/nine: Rewrite LOOP implementation, and a0 aL handling

Previous implementation didn't work well with nested loops.

Instead of using several address registers, put a0 and aL
into normal registers, and copy them to one address register when
we need to use them.

Wine tests loop_index_test() and nested_loop_test() now pass correctly.

Fixes r600g crash while loading Bioshock -
bug https://bugs.freedesktop.org/show_bug.cgi?id=85696

Tested-by: David Heidelberg <david@ixit.cz>
Reviewed-by: Tiziano Bacocco <tizbac2@gmail.com>
Signed-off-by: Axel Davy <axel.davy@ens.fr>
Cc: "10.4" <mesa-stable@lists.freedesktop.org>