sound: usb: Use IOMMU_CACHE mapping if USB controller is dma-coherent

If IO coherency for the USB controller is enabled, the shared buffers
need to be remapped with the cached attribute set so that the
controller HW can properly access the memory coherently. Otherwise,
the HW could end up reading stale data from cache.

While at it, remove the dma_sync_* calls, as they were previously
added with the misunderstanding that the APPS needs to force an
invalidation before passing it to the ADSP. This is not required
as long as the coherency settings are matched as there is no need
to manually perform cache maintenance when handing off the buffers.

Change-Id: I3a7ecbd7b7f1c264c64e9f5f82c9d4ec27848dc0
Signed-off-by: Jack Pham <jackp@codeaurora.org>