mb/esd: Get rid of device_t

Use of device_t has been abandoned in ramstage.

Change-Id: I5928e871b8e9ba5964c02fbabb7a9d8dc9ecc0a8
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/26082
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Rudolph <siro@das-labor.org>

src/mainboard/esd/atom15/mainboard.c

@@ -21,7 +21,7 @@
  * mainboard_enable is executed as first thing after enumerate_buses().
  * This is the earliest point to add customization.
  */
-static void mainboard_enable(device_t dev)
+static void mainboard_enable(struct device *dev)
 {
 }