ddr: altera: Clean up mem_config()

ddr: altera: Clean up mem_config()

Clean mem_config() function. First, reorder the math done in the
function such that WLAT and RLAT computation is together. Then,
scrap contradictory comments which do not match the result of the
math at all. Next, extract the mem_precharge_and_activate() call
from the end of the function as it is completely unrelated here.
Finally, rename the function to mem_init_latency().

Signed-off-by: Marek Vasut <marex@denx.de>