dmaengine: rcar-dmac: fix max_chunk_size for R-Car Gen3

According to R-Car Gen3 Rev.0.80 manual, the DMATCR can be set to 16,777,215 as maximum. So, this patch fixes the max_chunk_size for safety on all of SoCs. Otherwise, a system may hang if the DMATCR is set to 0 on R-Car Gen3.