pwm: lpss-*: Make use of devm_pwmchip_alloc() function

This prepares the pwm-lpss drivers to further changes of the pwm core
outlined in the commit introducing devm_pwmchip_alloc(). There is no
intended semantical change and the driver should behave as before.

Reviewed-by: Andy Shevchenko <andy@kernel.org>
Link: https://lore.kernel.org/r/b567ab5dd992e361eb884fa6c2cac11be9c7dde3.1707900770.git.u.kleine-koenig@pengutronix.de


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