mkimage: rockchip: add suport for rk33 serial

Add support for rockchip rk33 series Soc like rk3368 and rk3399

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/rkcommon.c b/tools/rkcommon.c
index 9ec7eb2..0a072aa 100644
--- a/tools/rkcommon.c
+++ b/tools/rkcommon.c
@@ -56,7 +56,7 @@
 static struct spl_info spl_infos[] = {
 	{ "rk3036", "RK30", 0x1000 },
 	{ "rk3288", "RK32", 0x8000 },
-	{ "rk33xx", "RK33", 0x20000 },
+	{ "rk3399", "RK33", 0x20000 },
 };
 
 static unsigned char rc4_key[16] = {