refactor(arm): allow platform specific SiP support

This patch introduces handler to add support for SiP calls to be
handled at EL3 for Arm platforms.

Consequently, the support for SPMD LSP is moved to corresponding
Arm platform SiP source file. This will allow us to add support
for a new SiP call in subsequent patch.

Change-Id: Ie29cb57fc622f96be3b67bebf34ce37cc82947d8
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>
5 files changed