samsung:board: dram_init(): alloc memory to store fdt dram info

samsung:board: dram_init(): alloc memory to store fdt dram info

For CONFIG_OF_MULTI the dram_init() function gets memory information
from the device tree blob by the call to fdtdec_decode_memory().
The same is done second time in dram_init_banksize() - this was the
simplest because board info structure is not initialized at dram_init()
stage.

This change uses malloc and gd->priv pointer to store the memory banks
parameters and next uses it in dram_init_banksize().

Thanks to this change, the boot time decreases, because, the function
fdtdec_decode_memory() is called only once.

Change-Id: I8f357c6a641d4440f32d2fe24d7e1e2dc5bc4a3d
Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>