ARM: imx6q: add the missing cko output selection

The clock output on imx6q CCM_CLKO1 pad is not always cko1 clock, and
there is a multiplexer to select between cko1 and cko2.  Add this
missing selection as the clock cko.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>