dw_dmac: fill optional encoded parameters in register structure

There is a block of the registers that are optional. However, if enabled they
contain useful information about the controller hardware configuration. We will
use this piece of data to autoconfigure the driver.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>