spi: imx: add fallback feature

Add fallback pio feature in case  dma transfer failed before start.
Besides, another whole pio transfer including setup_transfer will be
issued by spi core, no need to restore jobs like commit bcd8e776 ("spi:
imx: fallback to PIO if dma setup failure").

Signed-off-by: Robin Gong <yibin.gong@nxp.com>
Link: https://lore.kernel.org/r/1592347329-28363-3-git-send-email-yibin.gong@nxp.com


Signed-off-by: Mark Brown <broonie@kernel.org>