Get native wakelock stats from SystemSuspend if /sys/class/wakeup not available.

If /sys/class/wakeup is available, get both kernel and native wakelock
stats from SystemSuspend, else we get native wakelock stats from
SystemSuspend and fallback to /d/wakeup_sources for kernel wakelock
stats.

Bug: 128923994
Test: atest FrameworksCoreTests:KernelWakelockReaderTest
Test: Compare dumpsys suspend_control against
      dumpsys batterystats --checkin | grep kwl
      to verify BatteryStats is getting wakelock stats
      from SystemSuspend.

Change-Id: I08e56c984b903285bb965dd853dae4a63fdeb824