dt-bindings: arm: tegra: Add NVIDIA Tegra194 AXI2APB binding

Add device-tree binding documentation to represent the AXI2APB bridges
used by Control Backbone (CBB) 1.0 on Tegra194 SoCs. All errors for APB
slaves are reported as slave error because APB bas single bit to report
error. So, CBB driver needs to further check error status registers of
all the AXI2APB bridges to find error type.

Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>