firmware: arm_scmi: Add scmi_get_base_info()

Currently non-SCMI drivers cannot find out what the specific versions of
each SCMI provider implementation on the running system are.

However, different versions may use different ABIs (e.g. different clock
IDs), or behave different, requiring remapping or workarounds in other
drivers.

Add a public function to obtain base protocol information for the
selected SCMI provider.  This will be used by the R-Car X5H Clock Pulse
Generator and Module Controller drivers.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>