[ARM] CONFIG_DEBUG_STACK_USAGE

In early 2.6 days stack utilization instrumentation was made
configurable. Seems that arm misses the DEBUG_STACK_USAGE option.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>