libperfmgr: change to use Value directly in config

Using Value directly is more clear and intuitive than using an index of
Values.

Bug: 77282526
Test: libperfmgr_test and boot wahoo

(cherry picked from commit 4ea001c2d3dc3f5c8421a5e86098272b295b213e)

Change-Id: Id6bd284c431d347e36ba8ce2bb4c82a7a4924852
8 files changed