clk: msm: Add support to set desired duty-cycle for a clock

The API clk_set_duty_cycle allows a client to pass in a ratio
of (numerator/denominator) for the desired duty cycle of a clock.

Change-Id: I2868c1b4e69af6e53ff44048891d2786f68a8c0e
Signed-off-by: Taniya Das <tdas@codeaurora.org>