sf: Make IO modes at last in read modes

SLOW, FAST, DUAL, DUAL_IO, QUAD, QUAD_IO changed order to
SLOW, FAST, DUAL, QUAD, DUAL_IO, QUAD_IO

Cc: Simon Glass <sjg@chromium.org>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
Tested-by: Jagan Teki <jteki@openedev.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Jagan Teki <jteki@openedev.com>