ARM: imx: cm_fx6: remove sata init code from board file

Commit 5248930e ("dm: imx: cm_fx6: Enable more driver model support")
enabled driver model support for AHCI. Remove the old, now unused, sata
init code from the board file.

Signed-off-by: Christopher Spinrath <christopher.spinrath@rwth-aachen.de>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Simon Glass <sjg@chromium.org>