clk: ti: add support for clkctrl clocks

Until now the clkctrl clocks have been enabled/disabled through platform
routines. Thanks to this patch they can be enabled and configured directly
by the probed devices that need to use them.

For DT binding details see Linux doc:
- Documentation/devicetree/bindings/clock/ti-clkctrl.txt

Signed-off-by: Dario Binacchi <dariobin@libero.it>