tests: mem_protect/syscalls: move torture test to another group

This moves the syscall torture test into another test group or
suite so that we run the individual syscall tests first before
the torture test. If individual test fails, it is easier to see
the error. Especially under SMP where multiple CPUs can report
the same error, cluttering the output.

Also rename the test to syscall_switch_stress to better describe
its purpose.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>