Profiles: Optimize Crypto memory footprint in Profile Small

Optimize the memory footprint required by Crypto service in Profile
Small.

- Decrease the MAX number of concurrent multi-part operations to 4.
- Decrease the heap size used in backend crypto library since asymmetric
  cryptography is disabled.

Change-Id: If1b8d4b6cef098e132bd891a140be278993bf6c2
Signed-off-by: David Hu <david.hu@arm.com>