pwm: meson: Change prototype of a few 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 meson_pwm. To just not have to do
that, rework meson_pwm_calc(), meson_pwm_enable(), meson_pwm_disable()
and meson_pwm_init_channels() to take a pwm_chip.

Link: https://lore.kernel.org/r/157084e1dd464da0097edba880240868c1c0b27e.1707900770.git.u.kleine-koenig@pengutronix.de


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