ARM: samsung: select ATAGS where necessary

Most of the Samsung platforms do not yet allow building with
DT at all, so we should select CONFIG_ATAGS for now in all
cases we also select CONFIG_SAMSUNG_ATAGS.

Found during randconfig testing.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kukjin Kim <kgene.kim@samsung.com>
Cc: Tomasz Figa <tomasz.figa@gmail.com>
Cc: Ben Dooks <ben-linux@fluff.org>