glsl: Change do_set_program_inouts' is_fragment_shader arg to shader_type.

glsl: Change do_set_program_inouts' is_fragment_shader arg to shader_type.

This will allow us to add geometry shader support without having to
add another boolean argument.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>