Test: Updates on the PS test suite

1. Remove thread creation on test cases
2. Then only build the test helper and link "os_wrapper" only when NS
   ID management is enabled.
3. Remove unnecessary CMake library links - platform_region_defs.

Change-Id: I4ed42b0e44bdcda9262fff78d2c08a1d63b2ecc2
Signed-off-by: Kevin Peng <kevin.peng@arm.com>
4 files changed