clk: scmi: register scmi clocks with CCF

Implements SCMI APIs to retrieve the number exposed SCMI clocks using
SCMI_PROTOCOL_ATTRIBUTES messages and the names of the clocks using
SCMI_CLOCK_ATTRIBUTES messages.

This change updates sandbox SCMI clock test driver to manage these
2 new message IDs.

Cc: Lukasz Majewski <lukma@denx.de>
Cc: Sean Anderson <seanga2@gmail.com>
Cc: Clement Leger <clement.leger@bootlin.com>
Cc: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Signed-off-by: Gabriel Fernandez <gabriel.fernandez@st.com>
Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>