firmware: arm_scmi: Use asynchronous CLOCK_RATE_SET when possible

CLOCK_PROTOCOL_ATTRIBUTES provides attributes to indicate the maximum
number of pending asynchronous clock rate changes supported by the
platform. If it's non-zero, then we should be able to use asynchronous
clock rate set for any clocks until the maximum limit is reached.

Tracking the current count of pending asynchronous clock set rate
requests, we can decide if the incoming/new request for clock set rate
can be handled asynchronously or not until the maximum limit is
reached.

Cc: linux-clk@vger.kernel.org
Reviewed-by: Stephen Boyd <sboyd@kernel.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>