ENGR00231773-5 ASRC: use poll mode to receive last period of ASRC data

ASRC driver use DMA to transfer data from ASRC output FIFO to memory.
However, DMA way require the data number in ASRC output FIFO being larger
than watermark level. Thus a dma request can trigger a DMA burst. For
the last period of output data, its number is possiblely less than output
FIFO watermark level. In this case, the output DMA would pending for the
last period of output data until timeout.

In this patch:
	1 divide expected output data length into 2 parts: DMA part
and poll part. Using DMA to get the DMA part data and poll mode to
get the poll part.
	2 to prevent user from processing these 2 parts above, kernel
buffers would be untouchable. User application only need send its data
buffer address to driver instead of query the kernel buffer.

Signed-off-by: Chen Liangjun <b36089@freescale.com>

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