Fix use of conditional LMB

This code was not guarded with CONFIG_LMB so failed to build on x86.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/cmd_bootm.c b/common/cmd_bootm.c
index 4dbe952..f7595c0 100644
--- a/common/cmd_bootm.c
+++ b/common/cmd_bootm.c
@@ -537,7 +537,7 @@
 		}
 			break;
 #endif
-#if defined(CONFIG_OF_LIBFDT)
+#if defined(CONFIG_OF_LIBFDT) && defined(CONFIG_LMB)
 		case BOOTM_STATE_FDT:
 		{
 			boot_fdt_add_mem_rsv_regions(&images.lmb,