dm: core: Drop header files from dm/test.h

These header file should not be included in other header files. Remove
them and add to each individual file. Add test/test.h to test/ui.h since
that is a reasonable place.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/test/dm/led.c b/test/dm/led.c
index 00de7b3..3d5ad93 100644
--- a/test/dm/led.c
+++ b/test/dm/led.c
@@ -8,6 +8,7 @@
 #include <led.h>
 #include <asm/gpio.h>
 #include <dm/test.h>
+#include <test/test.h>
 #include <test/ut.h>
 
 /* Base test of the led uclass */