dm: rename device struct to udevice

using UBI and DM together leads in compiler error, as
both define a "struct device", so rename "struct device"
in include/dm/device.h to "struct udevice", as we use
linux code (MTD/UBI/UBIFS some USB code,...) and cannot
change the linux "struct device"

Signed-off-by: Heiko Schocher <hs@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Cc: Marek Vasut <marex@denx.de>
diff --git a/test/dm/gpio.c b/test/dm/gpio.c
index bf632bc..2b2b0b5 100644
--- a/test/dm/gpio.c
+++ b/test/dm/gpio.c
@@ -17,7 +17,7 @@
 {
 	unsigned int offset, gpio;
 	struct dm_gpio_ops *ops;
-	struct device *dev;
+	struct udevice *dev;
 	const char *name;
 	int offset_count;
 	char buf[80];