glsl: Add an option to clamp block indices when lowering UBO/SSBOs

glsl: Add an option to clamp block indices when lowering UBO/SSBOs

This prevents array overflow when the block is actually an array of UBOs or
SSBOs.  On some hardware such as i965, such overflows can cause GPU hangs.

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