pwm: stm32: Implementation of the waveform callbacks

Convert the stm32 pwm driver to use the new callbacks for hardware
programming.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://lore.kernel.org/r/332d4f736d8360038d03f109c013441c655eea23.1726819463.git.u.kleine-koenig@baylibre.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>

Author: ukleinek