dt-bindings: firmware: arm,scmi: Convert to json schema

Convert the old text format binding for System Control and Management Interface
(SCMI) Message Protocol into the new and shiny YAML format.

Cc: Cristian Marussi <cristian.marussi@arm.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Jim Quinlan <jim2101024@gmail.com>
Cc: Etienne Carriere <etienne.carriere@linaro.org>
Cc: Peter Hilber <peter.hilber@opensynergy.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Link: https://lore.kernel.org/r/20210604205710.1944363-5-sudeep.holla@arm.com


[robh: Rework interrupts schema and if/then]
Signed-off-by: Rob Herring <robh@kernel.org>