expo: Add basic tests

Add some tests for the expo, including setting up and rendering an expo.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/test/boot/Makefile b/test/boot/Makefile
index d724629..22ed61c 100644
--- a/test/boot/Makefile
+++ b/test/boot/Makefile
@@ -5,6 +5,8 @@
 obj-$(CONFIG_BOOTSTD) += bootdev.o bootstd_common.o bootflow.o bootmeth.o
 obj-$(CONFIG_FIT) += image.o
 
+obj-$(CONFIG_EXPO) += expo.o
+
 ifdef CONFIG_OF_LIVE
 obj-$(CONFIG_BOOTMETH_VBE_SIMPLE) += vbe_simple.o
 endif