dt-bindings: pwm: adi,axi-pwmgen: Fix clocks

dt-bindings: pwm: adi,axi-pwmgen: Fix clocks

Fix a shortcoming in the bindings that doesn't allow for a separate
external clock.

The AXI PWMGEN IP block has a compile option ASYNC_CLK_EN that allows
the use of an external clock for the PWM output separate from the AXI
clock that runs the peripheral.

This was missed in the original bindings and so users were writing dts
files where the one and only clock specified would be the external
clock, if there was one, incorrectly missing the separate AXI clock.

The correct bindings are that the AXI clock is always required and the
external clock is optional (must be given only when HDL compile option
ASYNC_CLK_EN=1).

Fixes: 1edf2c2a2841 ("dt-bindings: pwm: Add AXI PWM generator")
Cc: stable@vger.kernel.org
Signed-off-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20250529-pwm-axi-pwmgen-add-external-clock-v3-2-5d8809a7da91@baylibre.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>