dt-bindings: firmware: Add bindings for Tegra BPMP

The Boot and Power Management Processor (BPMP) is a co-processor found
in Tegra SoCs. It is designed to handle the early stages of the boot
process as well as to offload power management tasks (such as clocks,
resets, powergates, ...).

The binding document defines the resources that are used by the BPMP
firmware, which implements the interprocessor communication (IPC)
between the CPU and the BPMP.

Signed-off-by: Joseph Lo <josephl@nvidia.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>