pwm: Implement set period and duty cycle API

This allow the PWM QMSI shim driver to implement the set duty cycle
API, and correct the behavior of Set Value

Jira: ZEP-69 ZEP-156 ZEP-158

Change-Id: I47744958fed889116fbb5024343ea00f76ed7706
Signed-off-by: Sergio Rodriguez <sergio.sf.rodriguez@intel.com>
Signed-off-by: Baohong Liu <baohong.liu@intel.com>