driver/spi: fsl_qspi: Remove non-DM stuff

Convert fsl_qspi.c to complete DM mode.

Signed-off-by: Ashish Kumar <Ashish.Kumar@nxp.com>
Tested-by: Rajat Srivastava <rajat.srivastava@nxp.com>
Tested-by: Ye Li <ye.li@nxp.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>