pwm: Add a struct device to struct pwm_chip

This replaces the formerly dynamically allocated struct device. This
allows to additionally use it to track the lifetime of the struct
pwm_chip. Otherwise the new struct device provides the same sysfs API as
was provided by the dynamic device before.

Link: https://lore.kernel.org/r/35c65ea7f6de789a568ff39d7b6b4ce80de4b7dc.1710670958.git.u.kleine-koenig@pengutronix.de


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