dma: dw: add PCI part of the driver

This is the PCI part of the DesignWare DMAC driver. The controller is usually
used in the Intel hardware such as Intel Medfield.

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>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>