feat(spm): separate StMM SP specifics to add support for a S-EL0 SP

This patch separates the code from SPM_MM to get xlat table context and
move it to a common location. In addition, only APIs required from both
SPM_MM and FF-A EL3 SPMC are moved to the common location.

This allows understanding better what is required to support a S-EL0 SP
instead of trying to retrofit what already exists.

Signed-off-by: Achin Gupta <achin.gupta@arm.com>
Signed-off-by: Nishant Sharma <nishant.sharma@arm.com>
Change-Id: I142d7fbef5239869176d0de93842c66051d7ed78
5 files changed