Automatic merge from submit-queue (batch tested with PRs 55283, 55461, 55288, 53970, 55487). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
Add more comments for DevicePluginHandlerImpl struct
**What this PR does / why we need it**:
Add more comments
**Special notes for your reviewer**:
@jiayingz PTAL.
**Release note**:
```
NONE
```