imx: mx6sx enable SION for i2c pin mux

Enable IOMUX_CONFIG_SION for all I2C pin mux settings, otherwise
we will get erros when doing i2c operations.
error log like the following:
"
wait_for_sr_state: failed sr=81 cr=a0 state=2020
i2c_init_transfer: failed for chip 0xb retry=1
"

Signed-off-by: Peng Fan <Peng.Fan@freescale.com>