rockchip: add support for rk3288 PopMetal board

PopMetal is a rockchip rk3288 based board made by ChipSpark, which has
many interface such as HDMI, VGA, USB, micro-SD card, WiFi, Audio and
Gigabit Ethernet.

Signed-off-by: Ziyuan Xu <xzy.xu@rock-chips.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/dts/Makefile b/arch/arm/dts/Makefile
index cc0d6df..639c06d 100644
--- a/arch/arm/dts/Makefile
+++ b/arch/arm/dts/Makefile
@@ -33,6 +33,7 @@
 	rk3288-rock2-square.dtb \
 	rk3288-evb.dtb \
 	rk3288-fennec.dtb \
+	rk3288-popmetal.dtb \
 	rk3036-sdk.dtb \
 	rk3399-evb.dtb
 dtb-$(CONFIG_ARCH_MESON) += \