Added flag to enable subscription manager service through adb

Test: Boot up and basic phone testing
Test: adb root && adb shell device_config put telephony enable_subscription_manager_service true
      && adb shell device_config set_sync_disabled_for_tests persistent && sleep 3 && adb reboot
Fix: 266896752
Merged-In: Ib3b18b9a052de4d9f78e432f42b83d099f1b42a2
Change-Id: Ib3b18b9a052de4d9f78e432f42b83d099f1b42a2