ARM: SAMSUNG: Introduce SAMSUNG_ATAGS Kconfig entry

This patch adds a Kconfig entry that enables compilation of legacy
support code required for Samsung platforms that require ATAGS based
boot.

This allows to bypass compilation of this code when platforms without
ATAGS support are selected.

Signed-off-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>