device property: Introducing enum dev_dma_attr

A device could have one of the following DMA attributes:
    * DMA not supported
    * DMA non-coherent
    * DMA coherent

So, this patch introduces enum dev_dma_attribute. This will be used by
new APIs introduced in later patches.

Signed-off-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>