glsl: Store info about geometry shaders that emit vertices to non-zero streams.

glsl: Store info about geometry shaders that emit vertices to non-zero streams.

On Intel hardware when a geometry shader outputs GL_POINTS primitives we
only need to emit vertex control bits if it emits vertices to non-zero
streams, so use a flag to track this.

This flag will be set to TRUE when a geometry shader calls EmitStreamVertex()
or EndStreamPrimitive() with a non-zero stream parameter in a later patch.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>