of: Drop cpu.h include from of_device.h

Now that all users which had an implicit dependency on cpu.h have been
fixed. the cpu.h include can be dropped from of_device.h

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Rob Herring <[e-mail]>

include/linux/of_device.h

···
 #ifndef _LINUX_OF_DEVICE_H
 #define _LINUX_OF_DEVICE_H
 
-#include <linux/cpu.h>
 #include <linux/platform_device.h>
 #include <linux/of_platform.h> /* temporary until merge */