refactor(mediatek): update EMI stub implementation

Refactor EMI stub implementation with following changes.
- Move the SiP call handlers to TF-A upstream.
- Move EMI definition used by APUSYS to platform_def.h.
- Remove CONFIG_MTK_APUSYS_EMI_SUPPORT.

Change-Id: I30e1ee7f2ea2d6dc3415adba91cbe310af9b5eeb
Signed-off-by: Yidi Lin <yidilin@chromium.org>
10 files changed