dma: mmp-tdma: refine dma disable and dma-pos update

Below are the refinements.
1. Set DMA abort bit when disabling dma channel. This will clear
the remaining data in dma FIFO, to fix channel-swap issue.
2. Read DMA HW pointer when updating DMA status. Previously dma
position is calculated by adding one period size in dma interrupt.
This is inaccurate/insufficient for some high-quality audio APP.
Since interrupt bottom half handler has variable schedule delay,
it causes big error when calculating sample delay. Read the actual
HW pointer and feedback can improve the accuracy.
3. Do some minor code clean.

Signed-off-by: Qiao Zhou <zhouqiao@marvell.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>