vk/compiler: Set the binding table texture_start
vk/compiler: Set the binding table texture_start

This is by no means a complete solution to the binding table problems.
However, it does make texturing actually work.  Before, we were texturing
from the render target since they were both starting at 0.

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler