spi: imx: keep dma request disabled before dma transfer setup

spi: imx: keep dma request disabled before dma transfer setup

Since sdma hardware configure postpone to transfer phase, have to disable
dma request before dma transfer setup because there is a hardware
limitation on sdma event enable(ENBLn) as below:

"It is thus essential for the Arm platform to program them before any DMA
 request is triggered to the SDMA, otherwise an unpredictable combination
 of channels may be started."

Signed-off-by: Carlos Song <carlos.song@nxp.com>
Signed-off-by: Robin Gong <yibin.gong@nxp.com>
Link: https://patch.msgid.link/20251024055320.408482-1-carlos.song@nxp.com
Signed-off-by: Mark Brown <broonie@kernel.org>