MLK-11248: dmaengine: imx-sdma: add new api for sync with dma and substream

MLK-11248: dmaengine: imx-sdma: add new api for sync with dma and substream

There is occasion that dma callback come late after the substream is released.
Then there will be kernel dump.

[<805866b0>] (imx_pcm_dma_complete) from [<802fad9c>] (sdma_handle_channel_loop.isra.25+0x48/0x54)
[<802fad9c>] (sdma_handle_channel_loop.isra.25) from [<802fae48>] (sdma_tasklet+0xa0/0x1d4)
[<802fae48>] (sdma_tasklet) from [<800356e0>] (tasklet_action+0x64/0xf8)
[<800356e0>] (tasklet_action) from [<80034ea0>] (__do_softirq+0x104/0x218)
[<80034ea0>] (__do_softirq) from [<80035220>] (irq_exit+0xa8/0xec)
[<80035220>] (irq_exit) from [<8000ed44>] (handle_IRQ+0x3c/0x90)
[<8000ed44>] (handle_IRQ) from [<80008578>] (gic_handle_irq+0x28/0x5c)
[<80008578>] (gic_handle_irq) from [<80012100>] (__irq_svc+0x40/0x70)

The reason is the sdma tasklet is async with audio substream release. ALSA
think when terminate dma, the dma should be stopped and no callback be called.

This patch is to add new api dma_sync_wait_tasklet(), which is called in
snd_dmaengine_pcm_close(). It will make sure the callback not be called
after this funtion. Tasklet_kill is to wait scheduled tasklet end.

Tasklet_kill can't be added to terminate dma function, because terminate dma
function may be called in interrupt, but tasklet_kill can't be called in
interrupt context.

Signed-off-by: Shengjiu Wang <shengjiu.wang@freescale.com>
(cherry picked from commit 9815881b6acaa72a705e1fa3c26a852fc81bfce5)