drivers/pwm: add duty_ns and period_ns to core pwm chip
Add variables to control the duty_ns and period_ns of PWM
chips. When these variables are set, a call to either
pwm_enable() or pwm_config() is performed to enforce the
setup values.
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>