pwm: atmel-tcb: Put per-channel data into driver data

[ Upstream commit 78dca23b ]

This simplifies the code, reduces the number of memory allocations and
pointer dereferences.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Claudiu Beznea <claudiu.beznea@tuxon.dev>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
Stable-dep-of: 37f77070 ("pwm: atmel-tcb: Fix race condition and convert to guards")
Signed-off-by: Sasha Levin <sashal@kernel.org>