st/mesa: move blend color into its own state atom

This is now sensible thanks to the NewBlendColor flag.

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>

src/mesa/state_tracker/st_context.c

@@ -503,7 +503,7 @@ static void st_init_driver_flags(struct st_context *st)
    f->NewScissorTest = ST_NEW_SCISSOR | ST_NEW_RASTERIZER;
    f->NewAlphaTest = ST_NEW_DSA;
    f->NewBlend = ST_NEW_BLEND;
-   f->NewBlendColor = ST_NEW_BLEND; /* TODO: add an atom for blend color */
+   f->NewBlendColor = ST_NEW_BLEND_COLOR;
    f->NewColorMask = ST_NEW_BLEND;
    f->NewDepth = ST_NEW_DSA;
    f->NewLogicOp = ST_NEW_BLEND;