STMicroelectronics STM32 CEC driver

Required properties:
 - compatible : value should be "st,stm32-cec"
 - reg : Physical base address of the IP registers and length of memory
	 mapped region.
 - clocks : from common clock binding: handle to CEC clocks
 - clock-names : from common clock binding: must be "cec" and "hdmi-cec".
 - interrupts : CEC interrupt number to the CPU.

Example for stm32f746:

cec: cec@40006c00 {
	compatible = "st,stm32-cec";
	reg = <0x40006C00 0x400>;
	interrupts = <94>;
	clocks = <&rcc 0 STM32F7_APB1_CLOCK(CEC)>, <&rcc 1 CLK_HDMI_CEC>;
	clock-names = "cec", "hdmi-cec";
};