Add an stune group for NNAPI HAL

 - schedtune.prefer_idle 1
 - schedtune.boost 1

Test: mm
Test: configure NNAPI HAL to use nnapi-hal stune
Test: measure perf difference using MLTS benchmark

Change-Id: I5f467c6a58f2c1da40ec8276e101defc808854a3
(cherry picked from commit 1d748fea)