dmaengine: ti: edma: Add support for handling reserved channels

Like paRAM slots, channels could be used by other cores and in this case
we need to make sure that the driver do not alter these channels.

Handle the generic dma-channel-mask property to mark channels in a bitmap
which can not be used by Linux and convert the legacy rsv_chans if it is
provided by platform_data.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Link: https://lore.kernel.org/r/20191025073056.25450-4-peter.ujfalusi@ti.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>