pwm: airoha: Add support for EN7581 SoC

pwm: airoha: Add support for EN7581 SoC

Introduce driver for PWM module available on EN7581 SoC.

Limitations:
- Only 8 concurrent waveform generators are available for 8 combinations of
  duty_cycle and period. Waveform generators are shared between 16 GPIO
  pins and 17 SIPO GPIO pins.
- Supports only normal polarity.
- On configuration the currently running period is completed.
- Minimum supported period is 4 ms
- Maximum supported period is 1s

Signed-off-by: Benjamin Larsson <benjamin.larsson@genexis.eu>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Co-developed-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Co-developed-by: Christian Marangi <ansuelsmth@gmail.com>
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Link: https://patch.msgid.link/20251013103408.14724-1-ansuelsmth@gmail.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>