compiler/glsl: handle case where we have multiple users for types

Both Vulkan and OpenGL migth be using glsl_types simultaneously. Patch adds a one time init to track number of users and will release types only when last user calls _mesa_glsl_release_types.

This change fixes glsl_type memory leaks we have with anv driver.

Signed-off-by: Tapani Pälli tapani.palli@intel.com