rcar-hpbdma: add max transfer size

shdma_chan_probe() can set max transfer size,
but it will be PAGE_SIZE with out this patch.

Reviewed-by: Max Filippov <max.filippov@cogentembedded.com>
Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>