lmb: only force on arches that use it

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/include/asm-m68k/config.h b/include/asm-m68k/config.h
index 049c44e..36438be 100644
--- a/include/asm-m68k/config.h
+++ b/include/asm-m68k/config.h
@@ -21,4 +21,6 @@
 #ifndef _ASM_CONFIG_H_
 #define _ASM_CONFIG_H_
 
+#define CONFIG_LMB
+
 #endif