firmware: arm_ffa: Move constants to header file

FF-A function IDs and error codes will be needed in the hypervisor too,
so move to them to the header file where they can be shared. Rename the
version constants with an "FFA_" prefix so that they are less likely
to clash with other code in the tree.

Co-developed-by: Andrew Walbran <qwandor@google.com>
Signed-off-by: Andrew Walbran <qwandor@google.com>
Signed-off-by: Quentin Perret <qperret@google.com>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Link: https://lore.kernel.org/r/20221116170335.2341003-2-qperret@google.com


Signed-off-by: Will Deacon <will@kernel.org>