pwm: pca9685: Prepare removing pwm_chip from driver data

This prepares the driver for further changes that will drop struct
pwm_chip chip from struct pca9685. Use the pwm_chip as i2c client data
and gpiochip data instead of the pca9685 to get access to the
pwm_chip in pca9685_pwm_remove(), pca9685_pwm_runtime_suspend(),
pca9685_pwm_runtime_resume(), pca9685_pwm_gpio_request() and the gpio
callbacks without using pca->chip. Also the prototype for various helper
functions is changed to take a pwm_chip instead of a pca9685 for the
same reason.

Link: https://lore.kernel.org/r/e87b378545cee15a52f0d410fcceebf671ab90e0.1707900770.git.u.kleine-koenig@pengutronix.deSigned-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>