glsl: Convert piles of foreach_iter to the newer foreach_list macro.

glsl: Convert piles of foreach_iter to the newer foreach_list macro.

foreach_iter and exec_list_iterators have been deprecated for some time now;
we just hadn't ever bothered to convert code to the newer foreach_list
and foreach_list_safe macros.

In these cases, we aren't editing the list, so we can use foreach_list
rather than foreach_list_safe.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>