mm: umm_heap: Do not register Umem if CONFIG_BUILD_KERNEL=y

Summary:
- In the case of CONFIG_BUILD_KERNEL=y, showing Kmem and Page
  info is enough for free command

Impact:
- CONFIG_BUILD_KERNEL=y only

Testing:
- Tested with sabre-6quad:netknsh

Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

mm/umm_heap/umm_initialize.c

@@ -81,7 +81,11 @@
 
 void umm_initialize(FAR void *heap_start, size_t heap_size)
 {
+#ifdef CONFIG_BUILD_KERNEL
+  USR_HEAP = mm_initialize(NULL, heap_start, heap_size);
+#else
   USR_HEAP = mm_initialize("Umem", heap_start, heap_size);
+#endif
 }
 
 /****************************************************************************