anv: Implement vkCmdDispatchBase

This is part of the device groups extension/feature but it's a decent
chunk of work in its own right so it's worth breaking into its own
patch.  The mechanism we use is fairly straightforward: we just push the
base work group id into the shader and add it to the work group id we
get from dispatch.

Reviewed-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>

src/intel/vulkan/anv_cmd_buffer.c

@@ -688,6 +688,12 @@ anv_push_constant_value(struct anv_push_constants *data, uint32_t param)
       switch (param) {
       case BRW_PARAM_BUILTIN_ZERO:
          return 0;
+      case BRW_PARAM_BUILTIN_BASE_WORK_GROUP_ID_X:
+         return data->base_work_group_id[0];
+      case BRW_PARAM_BUILTIN_BASE_WORK_GROUP_ID_Y:
+         return data->base_work_group_id[1];
+      case BRW_PARAM_BUILTIN_BASE_WORK_GROUP_ID_Z:
+         return data->base_work_group_id[2];
       default:
          unreachable("Invalid param builtin");
       }