boards: nxp: mixmxrt1170_evk: Separate i2c6 from csi pin muxing

Pin muxing for i2c6 and csi should be separated as i2c is initialized
before csi. Otherwise, i2c6 bus device will not be ready when the
camera sensor on this bus initializes.

Signed-off-by: Phi Bang Nguyen <phibang.nguyen@nxp.com>