glsl: reduce buffer block duplication

glsl: reduce buffer block duplication

This reduces some of the craziness required for handling buffer
blocks. The problem is each shader stage holds its own information
about a block in memory, we were copying that information to a
program wide list but the per stage information remained meaning
when a binding was updated we needed to update all versions of it.

This changes the per stage blocks to instead point to a single
version of the block information in the program list.

Acked-by: Kenneth Graunke <kenneth@whitecape.org>