dma: tegra: add support for Tegra148/124

Tegra148 introduces a few changes to the APB DMA HW registers. Update the
driver to cope with them. Tegra124 inherits these changes.

* The register address stride between DMA channels increases.

* A new per-channel WCOUNT register is introduced.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Kunal Agrawal <kunala@nvidia.com>
[swarren, remove .dts file change, rewrote commit description, removed
some duplicate/unused code and register IO]
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Tested-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>