refactor(spm): managed exit tests

Factored out code to enable managed exit interrupt for a given SP, to
reuse it in the context of testing the Schedule Receiver Interrupt
SWd behavior, in the context of notifications feature work.

Signed-off-by: J-Alves <joao.alves@arm.com>
Change-Id: Idcecd486c7a952f0842ebf90c274adcea9e30152
3 files changed