hwc2.1: check sysfs node after request lhbm on or off am: feb967d0a7

Original change: https://googleplex-android-review.googlesource.com/c/platform/hardware/google/graphics/common/+/18906146

Change-Id: I9a4aec540b5360df60ec0ef73488d6d85fc12f57
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>