clk: add support for clocks provided by SCMI

On some ARM based systems, a separate Cortex-M based System Control
Processor(SCP) provides the overall power, clock, reset and system
control. System Control and Management Interface(SCMI) Message Protocol
is defined for the communication between the Application Cores(AP)
and the SCP.

This patch adds support for the clocks provided by SCP using SCMI
protocol.

Cc: linux-clk@vger.kernel.org
Cc: Michael Turquette <mturquette@baylibre.com>
Acked-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>