fix(el3-spmc): remove experimental flag

The EL3 SPMC is known to be deployed into end products and properly
tested since its introduction into TF-A v2.7.

Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
Change-Id: I96bb897cfefef20c33cfc39627b10746dce5485c
2 files changed