ARM: EXYNOS: Remove check for device tree presence

This patch makes the firmware setup code assume presence of DT, since it
is now the only way of booting supported for Exynos.

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>