feat: spm helper functions for MP tests

Added two helper functions to help with SPM tests in a MP setup.
- spm_core_sp_init: to initialize an SP in a given core.
- get_current_core_id: to get the current core ID.

Signed-off-by: J-Alves <joao.alves@arm.com>
Change-Id: Iad10d43f258f5ed05ce52b87c94a9333c228f26d
8 files changed