selftests: ifs: verify IFS scan test functionality

Two selftests are added to verify IFS scan test feature:

1. Perform IFS scan test once on each CPU using all the available image
   files.
2. Perform IFS scan test with the default image on a random cpu for 3
   rounds.

Reviewed-by: Jithu Joseph <jithu.joseph@intel.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Co-developed-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Signed-off-by: Pengfei Xu <pengfei.xu@intel.com>
Acked-by: Jithu Joseph <jithu.joseph@intel.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>