dmaengine: dw: Split DW and iDMA 32-bit operations

Here is a kinda big refactoring that should have been done
in the first place, when Intel iDMA 32-bit support appeared.

It splits operations which are different to Synopsys DesignWare and
Intel iDMA 32-bit controllers.

No functional change intended.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>