Extend the SDK Config.in file to explicitely declare a MODULES symbol with
the "option modules" flag set in order to prevent a kconfig segmentation fault
whenever a "depends m" dependency is encountered.
Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

Backport of r46514

git-svn-id: svn://svn.openwrt.org/openwrt/branches/chaos_calmer@46515 3c298f89-4303-0410-b956-a3cf2f4a3e73