dmaengine: dw: introduce generic filter function

The introduced filter function would be reused in the ACPI and DT cases since
in those cases we have to apply mandatory data to the requested channel. Thus,
patch moves platform driver to use it in that case.

The function unlikely can't be used by users of the driver due to an implicit
dependency to the dw_dmac_core module.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>