Add character-device based interface to inject and snoop SCMI bare messages
in little endian binary format: each injected message will be routed and
tracked by the normal SCMI core stack and any reply, regular or late, will
be provided on the same character-device used for injection.
This is meant to be used for testing and development purposes only,
definitely NOT in production: for these reasons when enabled, the normal
SCMI drivers operation is disrupted, unless SCMI_RAW_COEX option is also
enabled.
Testing tools, like the SCMI ACS compliance suite, can use this interface
to validate the SCMI platform Server implementation, or exercise the
freeBSD SCMI core stack layers.
Tested on: Arm Morello Board
Sponsored by: Arm Ltd
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>