dm: Rename U_BOOT_DRIVER_ALIAS to DM_DRIVER_ALIAS

We use the U_BOOT_ prefix (i.e. U_BOOT_DRIVER) to declare a driver but
in every other case we just use DM_. Update the alias macros to use the
DM_ prefix.

We could perhaps rename U_BOOT_DRIVER() to DM_DRIVER(), but this macro
is widely used and there is at least some benefit to indicating it us a
U-Boot driver, particularly for code ported from Linux. So for now, let's
keep that name.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/gpio/mxc_gpio.c b/drivers/gpio/mxc_gpio.c
index 6280fb5..06e6b22 100644
--- a/drivers/gpio/mxc_gpio.c
+++ b/drivers/gpio/mxc_gpio.c
@@ -345,7 +345,7 @@
 	.bind	= mxc_gpio_bind,
 };
 
-U_BOOT_DRIVER_ALIAS(gpio_mxc, fsl_imx6q_gpio)
+DM_DRIVER_ALIAS(gpio_mxc, fsl_imx6q_gpio)
 
 #if !CONFIG_IS_ENABLED(OF_CONTROL)
 static const struct mxc_gpio_plat mxc_plat[] = {