staging: greybus: pwm: Change prototype of helpers to prepare further changes

This prepares the driver for further changes that will make it harder to
determine the pwm_chip from a given gb_pwm_chip. To just not have
to do that, rework gb_pwm_activate_operation(),
gb_pwm_deactivate_operation(), gb_pwm_config_operation(),
gb_pwm_set_polarity_operation(), gb_pwm_enable_operation() and
gb_pwm_disable_operation() to take a pwm_chip. Also use the pwm_chip as
driver data instead of the gb_pwm_chip.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/ef9b346d5bab508d4ded81cf115bf244938d04f1.1707900770.git.u.kleine-koenig@pengutronix.de


Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>