dmaengine: add a driver for Intel integrated DMA 64-bit

Intel integrated DMA (iDMA) 64-bit is a specific IP that is used as a part of
LPSS devices such as HSUART or SPI. The iDMA IP is attached for private
usage on each host controller independently.

While it has similarities with Synopsys DesignWare DMA, the following
distinctions doesn't allow to use the existing driver:
- 64-bit mode with corresponding changes in Hardware Linked List data structure
- many slight differences in the channel registers

Moreover this driver is based on the DMA virtual channels framework that helps
to make the driver cleaner and easy to understand.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/dma/Kconfig

@@ -85,6 +85,14 @@ config INTEL_IOP_ADMA
 	help
 	  Enable support for the Intel(R) IOP Series RAID engines.
 
+config IDMA64
+	tristate "Intel integrated DMA 64-bit support"
+	select DMA_ENGINE
+	select DMA_VIRTUAL_CHANNELS
+	help
+	  Enable DMA support for Intel Low Power Subsystem such as found on
+	  Intel Skylake PCH.
+
 source "drivers/dma/dw/Kconfig"
 
 config AT_HDMAC