Instead of (arbitrarily?) spliting the per-chip driver data into two
structures, put everything into struct sti_pwm_chip. This reduces memory
management overhead and a few pointer indirections.

Link: https://lore.kernel.org/r/2788a421ec838ee8f63e76a78b04e1d48b49f959.1710068192.git.u.kleine-koenig@pengutronix.deSigned-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>