fix(coverity): enable SDEI support for imx8mn builds

Moreover, modify the default config for imx8mn build to enable
SDEI support.

Also, update the exclusion list to include the oem_svc.c file
which is no more used by any upstream platform.

Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>
Change-Id: I59793d81f7aa71a36a3de56ef8f58f25cd7ae4ef
4 files changed