ARM: i.MX53 Add the cko1, cko2 clock outputs.

These two clocks connect to external pins and can be muxed to
various internal clocks.
They are typically used either for debugging or to provide
clocks to external chips (eg audio codecs).

Currently only the selectable clocks that already exist in the clock tree
have been added.

Signed-off-by: Martin Fuzzey <mfuzzey@parkeon.com>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>