llvmpipe gles31 bits

This is 2 fixes I found while running deqp/glcts,

the first is a bit messy it adds gather component support to the tgsi paths, but I couldn't get llvm to extract the constant from the vector again, so had to side store the immediates.

The second is an alignment fix for tbos, this fixes some piglits as well. I've seen the format code generate instructions that require 32-byte aligned sources, so it makes sense to align this to 32 bytes.