Exynos5: Config: Place environment at the end of SPI flash

Exynos5: Config: Place environment at the end of SPI flash

Currently environment resides at the location where BL2 ends.
This may hold good in case there is an empty space at this
position. But what if this place already has a binary or is
expected to have one. To avoid such scenarios it is better
to save environment at the end of the flash.

Signed-off-by: Akshay Saraswat <akshay.s@samsung.com>
Acked-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>