In the device tree, the clock controller is a subnode of the firmware
node. Devices refer to the clocks by an id that is shared between the
ATF and the driver.

While the bindings for the clock controller are already upstream, the
device in mainline Linux does not use them, yet. Add them in the Barebox
device tree for now.

Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>