test: list: Add tests for hexdump.c

Add tests for the hex2bin, bin2hex, and hex_to_bin functions, which were
recently added to U-Boot.

Signed-off-by: Mario Six <mario.six@gdsys.cc>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/test/Makefile b/test/Makefile
index a5f52fd..1e43473 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -10,3 +10,4 @@
 obj-$(CONFIG_UT_TIME) += time_ut.o
 obj-$(CONFIG_UT_UNICODE) += unicode_ut.o
 obj-$(CONFIG_$(SPL_)LOG) += log/
+obj-$(CONFIG_UNIT_TEST) += lib/