ASoC: dmaengine_pcm: Make FLAG_NO_RESIDUE internal

Whether residue can be reported or not is not a property of the audio
controller but of the DMA controller. The FLAG_NO_RESIDUE was initially
added when the DMAengine framework had no support for describing the residue
reporting capabilities of the controller. Support for this was added quite a
while ago and recently the DMAengine framework started to complain if a
driver does not describe its capabilities and a lot of patches have been
merged that add support for this where it was missing. So it should be safe
to assume that driver on actively used platforms properly implement the DMA
capabilities API.

This patch makes the FLAG_NO_RESIDUE internal and no longer allows audio
controller drivers to manually set the flag. If a DMA driver against
expectations does not support reporting its capabilities for now the generic
DMAengine PCM driver will now emit a warning and simply assume that residue
reporting is not supported. In the future this might be changed to aborting
with an error.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@kernel.org>