firmware: arm_scmi: Add the raw mode co-existence support

When the raw support is enabled and configured in co-existence mode the
normal SCMI drivers are allowed to register with the SCMI core and
operate as usual alongside the raw operations.

SCMI normal and raw messages will be kept segregated from each other,
but only at the transaction level. Any further possible interference at
the protocol layer will have instead to be handled by the user to attain
reliable results while using the raw transactions.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Tested-by: Florian Fainelli <f.fainelli@gmail.com>
Tested-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20230118121426.492864-17-cristian.marussi@arm.com
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>