dt-bindings: dmaengine: dw-dmac: add protection control property

This patch for the DesignWare AHB Central
Direct Memory Access Controller adds the dma
protection control property:
	"snps,dma-protection-control"

as well as the properties specific values defines into
a new include file: include/dt-bindings/dma/dw-dmac.h

Note: The protection control signals are one-to-one
mapped to the AHB HPROT[1:3] signals for this controller.
The HPROT0 (Data Access) is always hardwired to 1.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Christian Lamparter <chunkeey@gmail.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>