spirv: Add tessellation varying and built-in support.

We need to:
- handle the extra array level for per-vertex varyings
- handle the patch qualifier correctly
- assign varying locations

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/compiler/spirv/vtn_private.h

@@ -280,6 +280,7 @@ struct vtn_variable {
    unsigned descriptor_set;
    unsigned binding;
    unsigned input_attachment_index;
+   bool patch;
 
    nir_variable *var;
    nir_variable **members;