pwm: bcm-kona: Implement .apply() callback

To eventually get rid of all legacy drivers convert this driver to the
modern world implementing .apply().

The conversion wasn't quite straight forward because .config() and
.enable() were special to effectively swap their usual order. This resulted
in calculating the required values twice in some cases when
pwm_apply_state() was called. This is optimized en passant, and the order
of the callbacks is preserved without special jumping through hoops.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>