Add support to get headroom from thermal cmd

Bug: 328306727
Test: adb shell cmd thermalservice headroom 20
Change-Id: Iab67a4947fcfa7027811c946d8d2d0c0e26fb4a1
(cherry picked from commit 71e4df07760dabdc30e7487b7fa0bdaf3697b8c7)
1 file changed