lmb: only force on arches that use it

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/include/asm-ppc/config.h b/include/asm-ppc/config.h
index 796707e..0d78aa4 100644
--- a/include/asm-ppc/config.h
+++ b/include/asm-ppc/config.h
@@ -21,6 +21,8 @@
 #ifndef _ASM_CONFIG_H_
 #define _ASM_CONFIG_H_
 
+#define CONFIG_LMB
+
 #ifndef CONFIG_MAX_MEM_MAPPED
 #if defined(CONFIG_4xx) || defined(CONFIG_E500) || defined(CONFIG_MPC86xx)
 #define CONFIG_MAX_MEM_MAPPED	((phys_size_t)2 << 30)