SMDK6400: Fix the mutiple link error

SMDK6400: Fix the mutiple link error

The first, the cpu_init.o have already been link for cmd_link_o_target
atfer compile, But, The link script re-link the point file. So the link
machine will generate multiple definition error information.

The second, Since the first 4kB of nand boot featue code move to nand_spl,
So It is not necessary to force the cpu_init.o in non-nand boot.

Signed-off-by: Zhong Hongbo <bocui107@gmail.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>