ARM: mvebu: a38x: use non-zero size for ddr scrubbing

Make ddr3_calc_mem_cs_size() global scope and use it in
ddr3_new_tip_ecc_scrub to correctly initialize all of DDR memory.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Signed-off-by: Stefan Roese <sr@denx.de>