pwm: Update pwm enable sequence in all PWM client drivers

The PWM controller in Qualcomm PMIC chipset needs to re-enabled
if the underlying PWM configuration is changed. With the
introduction of generic PWM framework in 3.10, the framework does not
pass through the PWM enable request if it finds that the PWM is
already enabled and silently discards the request. So add a check
to disable PWM before sending an enable request.

Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org>