rockchip: rk3399-gru: Fix include of TPL in u-boot.rom image

The chromebook specific u-boot.rom image does not include TPL when
building with TPL=y or ROCKCHIP_EXTERNAL_TPL=y.

Fix this by adding rockchip-tpl and u-boot-tpl nodes to the mkimage node
for the u-boot.rom binman image.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>

arch/arm/dts/rk3399-u-boot.dtsi

@@ -39,6 +39,14 @@
 
 		mkimage {
 			args = "-n rk3399 -T rkspi";
+			multiple-data-files;
+#ifdef CONFIG_ROCKCHIP_EXTERNAL_TPL
+			rockchip-tpl {
+			};
+#elif defined(CONFIG_TPL)
+			u-boot-tpl {
+			};
+#endif
 			u-boot-spl {
 			};
 		};