rockchip: Allow jerry to use of-platdata

This board always boots from SPI, so update the code to support that with
of-platdata. The boot source is not currently available with of-platdata.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/mach-rockchip/rk3288-board-spl.c b/arch/arm/mach-rockchip/rk3288-board-spl.c
index 0f40351..185b5fd 100644
--- a/arch/arm/mach-rockchip/rk3288-board-spl.c
+++ b/arch/arm/mach-rockchip/rk3288-board-spl.c
@@ -64,6 +64,8 @@
 	}
 
 fallback:
+#elif defined(CONFIG_TARGET_CHROMEBOOK_JERRY)
+	return BOOT_DEVICE_SPI;
 #endif
 	return BOOT_DEVICE_MMC1;
 }