firmware: scmi: add support for clock management protocol

This includes:
	1) Source containing helper functions, each
	implementing a command from the clock management
	protocol.

	2) A clock controller driver making use of said
	helper functions and implementing the clock
	subsystem API.

	3) A DT binding for clock protocol node.

Signed-off-by: Laurentiu Mihalcea <laurentiu.mihalcea@nxp.com>