dt-bindings: leds: Add Texas Instruments TPS6131x flash LED driver

Document Texas Instruments TPS61310/TPS61311 flash LED driver devicetree
bindings.

Signed-off-by: Matthias Fend <matthias.fend@emfend.at>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20250514-leds-tps6131x-v5-1-a4fb9e7f2c47@emfend.at


Signed-off-by: Lee Jones <lee@kernel.org>