nir: Add per_view attribute to nir_variable

If a nir_variable is tagged with per_view, it must be an array with
size corresponding to the number of views.  For slot-tracking, it is
considered to take just the slot for a single element -- drivers will
take care of expanding this appropriately.

This will be used to implement the ability of having per-view position
in a vertex shader in Intel platforms.

Acked-by: Rafael Antognolli <rafael.antognolli@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/2313>

src/compiler/nir/nir_validate.c

@@ -1134,6 +1134,9 @@ validate_var_decl(nir_variable *var, nir_variable_mode valid_modes,
       validate_assert(state, var->members != NULL);
    }
 
+   if (var->data.per_view)
+      validate_assert(state, glsl_type_is_array(var->type));
+
    /*
     * TODO validate some things ir_validate.cpp does (requires more GLSL type
     * support)