parisc: Reduce thread stack to 16 kb

In testing, I found that the thread stack can be 16 kB when using an irq
stack.  Without it, the thread stack needs to be 32 kB. Currently, the irq
stack is 32 kB. While it probably could be 16 kB, I would prefer to leave it
as is for safety.
Signed-off-by: John David Anglin <dave.anglin@bell.net>
Signed-off-by: Helge Deller <deller@gmx.de>

arch/parisc/include/asm/thread_info.h

@@ -35,7 +35,12 @@ struct thread_info {
 
 /* thread information allocation */
 
+#ifdef CONFIG_IRQSTACKS
+#define THREAD_SIZE_ORDER	2 /* PA-RISC requires at least 16k stack */
+#else
 #define THREAD_SIZE_ORDER	3 /* PA-RISC requires at least 32k stack */
+#endif
+
 /* Be sure to hunt all references to this down when you change the size of
  * the kernel stack */
 #define THREAD_SIZE             (PAGE_SIZE << THREAD_SIZE_ORDER)