Move concat define to the one place that needs it.

include/dev/driver.h

Index: include/dev/driver.h
diff --git a/include/dev/driver.h b/include/dev/driver.h
index c45cac85a4842efa3d7c180caa670610a03b463b..3622fea296c279e32f9d19641643bcc294575802 100644
--- a/include/dev/driver.h
+++ b/include/dev/driver.h
@@ -68,6 +68,10 @@ struct driver {
     const struct driver_ops *ops;
 };
 
+/* macro-expanding concat */
+#define concat(a, b) __ex_concat(a, b)
+#define __ex_concat(a, b) a ## b
+
 #define DRIVER_EXPORT(type_, ops_) \
     const struct driver concat(__driver_, type_) \
         __ALIGNED(sizeof(void *)) __SECTION(".drivers") = { \