dma: dw: split driver to library part and platform code

To simplify the driver development let's split driver to library and platform
code parts. It helps us to add PCI driver in future.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
[Fixed compile error and few checkpatch issues]
Signed-off-by: Vinod Koul <vinod.koul@intel.com>