arm: shannon_defconfig: disable IDE subsystem

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

Cc: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>