dmaengine: dw: we do support Merrifield SoC in PCI mode

Intel Merrifield platform contains Intel integrated DMA (iDMA 32-bit) which has
a slightly different register mapping, e.g. some bits in CTL_* and CFG_*
channel registers, and has to use platform data since there is no
autoconfiguration.

The iDMA 32-bit specification is available in the publicly available
documentation for Intel Braswell and BayTrail SoCs as LPE Audio DMA.

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