Add VIRGL_BIND_SHADER_BUFFER
The guest needs to always mark SSBOs as unclean, since it's possible the shader can write to them without doing a transfer.
We don't necessarily need to add VIRGL_BIND_SHADER_BUFFER, and we can do this just with PIPE_BIND_SHADER_BUFFER, but this seemed most consistent with prior commits.
With some host side changes too, fixes:
dEQP-GLES31.functional.shaders.builtin_var.compute.num_work_groups