misc: fastrpc: make sure memory read and writes are visible

dma_alloc_coherent buffers could have writes queued in store buffers so
commit them before sending buffer to DSP using correct dma barriers.
Same with vice-versa.

Fixes: c68cfb71 ("misc: fastrpc: Add support for context Invoke method")
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>