Use system package name for SYSTEM_UID in the BatteryEntry

Force use the system package for the SYSTEM_UID, since the SYSTEM_UID is
used for multiple packages. The getPackageWithHighestDrain() method may
get different packages to represent it, since it will use the highest
battery drain to represent the SYSTEM_UID if there are multiple packages
use the same UID value to make users confuse about the usage data.
_
$ adb shell pm list packages --uid 1000
package:android uid:1000
package:com.android.dynsystem uid:1000
package:com.android.frameworks.core.batterystatsviewer uid:1000
package:com.android.inputdevices uid:1000
package:com.android.keychain uid:1000
package:com.android.localtransport uid:1000
package:com.android.location.fused uid:1000
package:com.android.providers.settings uid:1000
package:com.android.server.telecom uid:1000
package:com.android.settings uid:1000
package:com.android.wallpaperbackup uid:1000

Bug: 202682426
Test: make RunSettingsRoboTests -j56 ROBOTEST_FILTER="com.android.settings.fuelgauge"
Change-Id: I447bfa1b32037763a2194c0639abcc334c7d8b78