parisc,metag: Implement CONFIG_DEBUG_STACK_USAGE option

On parisc and metag the stack grows upwards, so for those we need to
scan the stack downwards in order to calculate how much stack a process
has used.

Tested on a 64bit parisc kernel.

Signed-off-by: Helge Deller <deller@gmx.de>

lib/Kconfig.debug

@@ -558,7 +558,7 @@ config DEBUG_KMEMLEAK_DEFAULT_OFF
 
 config DEBUG_STACK_USAGE
 	bool "Stack utilization instrumentation"
-	depends on DEBUG_KERNEL && !IA64 && !PARISC && !METAG
+	depends on DEBUG_KERNEL && !IA64
 	help
 	  Enables the display of the minimum amount of free stack which each
 	  task has ever had available in the sysrq-T and sysrq-P debug output.