pwm: Add kernel doc for members added to pwm_ops recently

The callbacks for lowlevel pwm drivers were expanded to handle the new
waveform abstraction. When doing that I missed to expand the kernel doc
description. This is catched up here.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Link: https://lore.kernel.org/linux-next/20241001135207.125ca7af@canb.auug.org.au
Fixes: 17e40c2 ("pwm: New abstraction for PWM waveforms")
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Link: https://lore.kernel.org/r/20241001085138.1025818-2-u.kleine-koenig@baylibre.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>

Author: ukleinek

include/linux/pwm.h

@@ -276,6 +276,11 @@ struct pwm_capture {
  * @request: optional hook for requesting a PWM
  * @free: optional hook for freeing a PWM
  * @capture: capture and report PWM signal
+ * @sizeof_wfhw: size (in bytes) of driver specific waveform presentation
+ * @round_waveform_tohw: convert a struct pwm_waveform to driver specific presentation
+ * @round_waveform_fromhw: convert a driver specific waveform presentation to struct pwm_waveform
+ * @read_waveform: read driver specific waveform presentation from hardware
+ * @write_waveform: write driver specific waveform presentation to hardware
  * @apply: atomically apply a new PWM config
  * @get_state: get the current PWM state.
  */