SPM: Optimize stateless service logic

- Rename the variables to make more sense.
- Do not chain stateless services as they are never looked up.
- Fine-tune the bit definition of service flags.

Change-Id: Ie242ceefa0a9b43581d12963a92e59c6da3fa3af
Signed-off-by: Ken Liu <Ken.Liu@arm.com>
9 files changed