ARM: tegra: add IVC protocol implementation

IVC (Inter-VM Communication) protocol is a Tegra-specific IPC (Inter
Processor Communication) framework. Within the context of U-Boot, it is
typically used for communication between the main CPU and various
auxiliary processors. In particular, it will be used to communicate with
the BPMP (Boot and Power Management Processor) on Tegra186 in order to
manipulate clocks and reset signals.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>