dt-bindings: dma: ti: k3-*: Add descriptions for register regions

In preparation for introducing more register regions, add description
for existing register regions so that its easier to map reg-names to
that of SoC Documentations/TRMs.

Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20231124045722.191817-2-vigneshr@ti.com


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