Use System.nanoTime instead of SystemClock for benchmarks

Make sure we use the same system clock used by BenchmarkState when we
measure the benchmark latency manually with the manual one.

Bug: 433734537
Flag: android.os.vibrator.remove_hidl_support
Test: VibratorPerfTest
Change-Id: I47b6a356e5ddbd7a61230d1f5f1582c8aa883114