feat(interrupts): resume interrupted target vCPU

An SP could be interrupted by a NS interrupt whilst handling a direct
message request from another SP. The target SP could send a managed
exit response, if supported.

Consequently, the sender of the direct message request resumes the
target SP by allocating CPU cycles using dummy direct message request.

Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>
Change-Id: I697aeb189da12850af9a1db4c3e3e550b5b36541
1 file changed