pwm: Add driver for AXI PWM generator

pwm: Add driver for AXI PWM generator

Add support for the Analog Devices AXI PWM Generator. This device is an
FPGA-implemented peripheral used as PWM signal generator and can be
interfaced with AXI4. The register map of this peripheral makes it
possible to configure the period and duty cycle of the output signal.

Link: https://analogdevicesinc.github.io/hdl/library/axi_pwm_gen/index.html
Co-developed-by: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
Co-developed-by: David Lechner <dlechner@baylibre.com>
Signed-off-by: David Lechner <dlechner@baylibre.com>
Signed-off-by: Drew Fustini <dfustini@baylibre.com>
Acked-by: Nuno Sa <nuno.sa@analog.com>
Co-developed-by: Trevor Gamblin <tgamblin@baylibre.com>
Signed-off-by: Trevor Gamblin <tgamblin@baylibre.com>
Link: https://lore.kernel.org/r/20240605203507.1934434-3-tgamblin@baylibre.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>