Add PACKAGE_USAGE_STATS permission to shell.

This is needed for calling AM.registerUidObserver.

Fixes: 64400666
Test: cts-tradefed run singleCommand cts-dev -m CtsAppTestCases -t \
      android.app.cts.ActivityManagerProcessStateTest
Change-Id: I4f500d0d8d516b6b8961ea2f8c083add3ae949a9