rockchip: jerry: Add serial support

This option allows the serial console to work correctly. Add it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/chromebook_jerry_defconfig b/configs/chromebook_jerry_defconfig
index 5c70957..c45bc22 100644
--- a/configs/chromebook_jerry_defconfig
+++ b/configs/chromebook_jerry_defconfig
@@ -85,6 +85,7 @@
 CONFIG_RAM=y
 CONFIG_SPL_RAM=y
 CONFIG_DEBUG_UART_SHIFT=2
+CONFIG_ROCKCHIP_SERIAL=y
 CONFIG_SOUND=y
 CONFIG_I2S=y
 CONFIG_I2S_ROCKCHIP=y