ARM: mx27: Replace clk_register_clkdev with clock DT lookup

Similarly as it was done for mx6q, use a DT lookup in order to make maintainance
task for the clock devices easier.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Tested-by: Markus Pargmann <mpa@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>