tracing: power: Define clock_set_rate_complete trace event

clk_set_rate event involves a variable overhead due to a
number of additional operations needed (regulator set voltage
operations, etc). Since the overhead may differ based on a
number of factors, add a clk_set_rate event so as to enable
recording of clk_set_rate operation latency.

Change-Id: Ie5c0ab1929f32e08b04d2a255e631c95a68e49fc
Signed-off-by: Devesh Jhunjhunwala <deveshj@codeaurora.org>