slimbus: ngd: dt-bindings: Add slim ngd dt bindings

This patch adds bindings for Qualcomm SLIMBus NGD controller.
SLIMBus NGD controller is a light-weight driver responsible for
communicating with SLIMBus slaves directly over the bus using messaging
interface and communicating with master component residing on ADSP for
bandwidth and data-channel management

Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Tested-by: Craig Tatlor <ctatlor97@gmail.com>
Reviewed-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>