power/stats: Adding subsystem field to Channel am: e3dfa5b158 am: 4c23c6892a

Original change: https://android-review.googlesource.com/c/platform/hardware/interfaces/+/1576531

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I07d072d96d9edb27414ca207e030683f0b1711ec