firmware: arm_ffa: Add support for FFA_MSG_SEND2

firmware: arm_ffa: Add support for FFA_MSG_SEND2

The FFA_MSG_SEND2 can be  used to transmit a partition message from
the Tx buffer of the sender(the driver in this case) endpoint to the Rx
buffer of the receiver endpoint.

An invocation of the FFA_MSG_SEND2 transfers the ownership of the Tx
buffer to the receiver endpoint(or any intermediate consumer). Completion
of an FFA_MSG_SEND2 invocation transfers the ownership of the buffer
back to the sender endpoint.

The framework defines the FFA_MSG_SEND2 interface to transmit a partition
message from the Tx buffer of the sender to the Rx buffer of a receiver
and inform the scheduler that the receiver must be run.

Link: https://lore.kernel.org/r/20240417090931.2866487-1-sudeep.holla@arm.com
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>