SMDKV310: use get_ram_size() to validate dram size

smdkv310.c: in dram_init_banksize(void) function dram size was
initialized without validation. get_ram_size() function will
validate the bank size before initialization.

Signed-off-by: Chander Kashyap <chander.kashyap@linaro.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>