dt-bindings: pwm: thead: Add T-HEAD TH1520 PWM controller

dt-bindings: pwm: thead: Add T-HEAD TH1520 PWM controller

Add the Device Tree binding documentation for the T-HEAD
TH1520 SoC PWM controller.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Drew Fustini <fustini@kernel.org>
Reviewed-by: Elle Rhumsaa <elle@weathered-steel.dev>
Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>
Link: https://patch.msgid.link/20251016-rust-next-pwm-working-fan-for-sending-v16-5-a5df2405d2bd@samsung.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>