ddr: altera: Stratix10: Add ECC memory scrubbing

Scrub memory content if ECC is enabled and it is not
from warm reset boot.

Enable icache and dcache before scrub memory
and use "DC ZVA" instruction to clear memory
to zeros. This instruction writes a cache line
at a time and it can prevent false ECC error
trigger if write cache line partially.

Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>