staging: greybus: introduce pwm_ops::apply

Introduce newer .apply function in pwm_ops to replace legacy operations
including enable, disable, config and set_polarity.

This guarantees atomic changes of the pwm controller configuration.

Reviewed-by: Alex Elder <elder@linaro.org>
Signed-off-by: Song Chen <chensong_2000@189.cn>
Link: https://lore.kernel.org/r/1647597432-27586-1-git-send-email-chensong_2000@189.cn


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>