Add dma-channel-mask property in Tegra GPCDMA document.

The property would help to specify the channels to be used in
kernel and reserve few for the firmware. This was previously
achieved by limiting the channel number to 31 in the driver.
This is wrong and does not align with the hardware. Correct
this and set the max interrupts to 32.
Signed-off-by: Akhil R <akhilrajeev@nvidia.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20221110171748.40304-2-akhilrajeev@nvidia.comSigned-off-by: Vinod Koul <vkoul@kernel.org>