dt-bindings: dma: ti: k3-pktdma: Describe cfg register regions

Packet DMA (PKTDMA) module on K3 SoCs have ring cfg, TX and RX channel
cfg and RX flow cfg register regions which are usually configured by a
Device Management firmware. But certain entities such as bootloader
(like U-Boot) may have to access them directly. Describe this region in
the binding documentation for completeness of module description.

Keep the binding compatible with existing DTS files by requiring first
four regions to be present at least.

Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20231124045722.191817-4-vigneshr@ti.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>