arm: mainstone_defconfig: disable IDE subsystem

This patch disables deprecated IDE subsystem in mainstone_defconfig
(no IDE host drivers are selected in this config so there is no valid
reason to enable IDE subsystem itself).

Cc: Daniel Mack <daniel@zonque.org>
Cc: Haojian Zhuang <haojian.zhuang@gmail.com>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>

arch/arm/configs/mainstone_defconfig

@@ -27,7 +27,6 @@ CONFIG_MTD_CFI_ADV_OPTIONS=y
 CONFIG_MTD_CFI_GEOMETRY=y
 # CONFIG_MTD_CFI_I1 is not set
 CONFIG_MTD_CFI_INTELEXT=y
-CONFIG_IDE=y
 CONFIG_NETDEVICES=y
 CONFIG_NET_ETHERNET=y
 CONFIG_SMC91X=y