firmware: arm_ffa: Implement the FFA_RUN interface

FFA_RUN is used by a scheduler to allocate CPU cycles to a target
endpoint execution context specified in the target information parameter.

If the endpoint execution context is in the waiting/blocked state, it
transitions to the running state.

Expose the ability to call FFA_RUN in order to give any partition in the
system cpu cycles to perform IMPDEF functionality.

Link: https://lore.kernel.org/r/20231005-ffa_v1-1_notif-v4-4-cddd3237809c@arm.com


Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>