test: Add tests for the extcon

Provide tests to the simple extcon device.

Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/test/dm/Makefile b/test/dm/Makefile
index c8534b5..3799b1a 100644
--- a/test/dm/Makefile
+++ b/test/dm/Makefile
@@ -49,6 +49,7 @@
 obj-$(CONFIG_ECDSA_VERIFY) += ecdsa.o
 obj-$(CONFIG_EFI_MEDIA_SANDBOX) += efi_media.o
 obj-$(CONFIG_DM_ETH) += eth.o
+obj-$(CONFIG_EXTCON) += extcon.o
 ifneq ($(CONFIG_EFI_PARTITION),)
 obj-$(CONFIG_FASTBOOT_FLASH_MMC) += fastboot.o
 endif