expo: Move cedit test into its own file and tidy

Move this test out so it can have its own file. Rename the test to use
a cedit_ prefix.

This allows us to drop the check for CONFIG_CMD_CEDIT in the test.

Also we don't need driver model objects for this test, so drop them.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/test/boot/Makefile b/test/boot/Makefile
index 22ed61c..5294758 100644
--- a/test/boot/Makefile
+++ b/test/boot/Makefile
@@ -6,6 +6,7 @@
 obj-$(CONFIG_FIT) += image.o
 
 obj-$(CONFIG_EXPO) += expo.o
+obj-$(CONFIG_CEDIT) += cedit.o
 
 ifdef CONFIG_OF_LIVE
 obj-$(CONFIG_BOOTMETH_VBE_SIMPLE) += vbe_simple.o