ANDROID: sched: consider stune boost margin when computing energy

If CONFIG_SCHED_TUNE is enabled, it does not use boosted cpu util
to compute energy, so it could not reflect the real freq when a
cpu has boosted tasks on it. Addressing it by adding boost margin
if type is FREQUENCY_UTIL in schedutil_cpu_util().

Bug: 158637636
Signed-off-by: Rick Yiu <rickyiu@google.com>
Change-Id: I570920cb1e67d07de87006fca058d50e9358b7cd