MLK-9986-4 dma: imx-sdma: add new ecspi tx script

Current ecspi rom script didn't take care of rxfifo overflow risk. Add new
ecspi tx script to check the rxfifo status, if it is near to full(>=48 bytes),
do not copy data to txfifo which will trigger data push into rxfifo. Because
rx script may not read rxfifo in time, we have to consider it.

Signed-off-by: Robin Gong <b38343@freescale.com>
(cherry picked from commit 17f472aa698aba0af5da4566df447e23306f4289)
(cherry picked from commit 90c929d7d1a3f8e196641b5ed7a33d2ee03bd63c)