pwm: QMSI PWM driver

This creates the QMSI PWM driver which is simply a shim driver based
on the PWM driver provided by QMSI BSP.

In order to enable this driver, the following options should be set:
CONFIG_QMSI_DRIVERS=y
CONFIG_QMSI_INSTALL_PATH="/path/to/libqmsi/directory"
CONFIG_PWM=y
CONFIG_PWM_QMSI=y

Optionally this can be set:
CONFIG_PWM_QMSI_NUM_PORTS=Number of ports available, default is 1

Origin of the file: This file has been created from scratch

Change-Id: Icac90154d020babca1c11147056a3438b84b0d3f
Signed-off-by: Sergio Rodriguez <sergio.sf.rodriguez@intel.com>