sparseirq: fix numa_migrate_irq_desc dependency and comments

Impact: reduce kconfig variable scope and clean up

Bartlomiej pointed out that the config dependencies and comments are not right.

update it depend to NUMA, and fix some comments

Reported-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/irq/numa_migrate.c

@@ -1,13 +1,8 @@
 /*
- * linux/kernel/irq/handle.c
- *
- * Copyright (C) 1992, 1998-2006 Linus Torvalds, Ingo Molnar
- * Copyright (C) 2005-2006, Thomas Gleixner, Russell King
- *
- * This file contains the core interrupt handling code.
- *
- * Detailed information is available in Documentation/DocBook/genericirq
+ * NUMA irq-desc migration code
  *
+ * Migrate IRQ data structures (irq_desc, chip_data, etc.) over to
+ * the new "home node" of the IRQ.
  */
 
 #include <linux/irq.h>