dmaengine: dw-edma: Use non-atomic io-64 methods

Instead of splitting 64-bits IOs up into two 32-bits ones, use the existing
non-atomic readq()/writeq() functions. By doing so we can discard
CONFIG_64BIT #ifdefs from the code.

Tested-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Acked-by: Vinod Koul <vkoul@kernel.org>