Add new core SCMI transfer operations based on protocol handles to
enable protocols to builds and send their own protocol specific messages.

Keep old original scmi_xfer_ operations interface as wrappers around the
new interface in order to let coexist old and new interfaces to ease
protocol by protocol migration.

In order to support such migration the above wrappers and some
additional transient code is also introduced in this commit. It will be
later removed as a whole once the full migration of protocols and SCMI
drivers will have been completed.

Link: https://lore.kernel.org/r/20210316124903.35011-9-cristian.marussi@arm.comTested-by: NFlorian Fainelli <f.fainelli@gmail.com>
Signed-off-by: NCristian Marussi <cristian.marussi@arm.com>
Signed-off-by: NSudeep Holla <sudeep.holla@arm.com>