dmaengine: ioat: fixing chunk sizing macros dependency

changing macros which assumption is chunk size of 2M,
which can be other size
prepare for changing allocation chunk size.

Acked-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Leonid Ravich <Leonid.Ravich@emc.com>
Link: https://lore.kernel.org/r/20200416170628.16196-1-leonid.ravich@dell.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>