MLK-10502-2 spi: imx: use tc interrupt for the tail data in DMA mode

Use transfer complete interrupt for the tail data instead of PIO read.
Some slave devices may not send data timely while checking rxfifo status, that means
some tail data may loss. TC interrupt ensure no any data lossing.

Signed-off-by: Robin Gong <b38343@freescale.com>
(cherry picked from commit a8470bc29940ae46454b509014341726714b6e25)