ARM: 6872/1: arch:common:Makefile Remove unused config in the Makefile.

The patch below removes an unused config variable found by using a kernel
cleanup script.

Signed-off-by: Justin P. Mattock <justinmattock@gmail.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>