selftests: amd-pstate: Rename amd-pstate-ut.sh to basic.sh.

Rename amd-pstate-ut.sh to basic.sh.
The purpose of this modification is to facilitate the subsequent
addition of gitsource, tbench and other tests.

Signed-off-by: Meng Li <li.meng@amd.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>