dt-bindings: dma: Add lpc32xx DMA mux binding

LPC32XX SoCs use pl080 dma controller which have few request signals
multiplexed between peripherals. This binding describes how devices can
use the multiplexed request signals.

Signed-off-by: Piotr Wojtaszczyk <piotr.wojtaszczyk@timesys.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20240627150046.258795-3-piotr.wojtaszczyk@timesys.com


Signed-off-by: Rob Herring (Arm) <robh@kernel.org>