Exynos5: ddr3: Choose between single or double channel config

Exynos5: ddr3: Choose between single or double channel config

Add a 4G configuration and choose it based on the number of banks
declared in config file. A board with 4 SDRAM banks declared (as
per CONFIG_NR_DRAM_BANKS) will end up with the 2G confiuration.

Signed-off-by: Doug Anderson <dianders@chromium.org>
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>