firmware: arm_scmi: Rename scmi_{msg_,}clock_config_{get,set}_{2,21}

It is very confusing to use *_v2 for everything applicable until SCMI
clock protocol version v2.0 including v1.0 for example. So let us rename
such that *_v2 is used only for SCMI clock protocol v2.1 onwards. Also
add comment to indicate the same explicitly.

Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>
Link: https://lore.kernel.org/r/20230925101557.3839860-1-sudeep.holla@arm.com


Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>