developer-options: avoid oem-unlock preference controller crash

If there is no FEATURE_TELEPHONY_CARRIERLOCK.

BUG: 123583878

Test: lunch sdk_phone_x86-eng
make -j
emulator
the Settings->System->Developer options should not crash

Test:
make RunSettingsRoboTests ROBOTEST_FILTER=OemUnlockPreferenceControllerTest
should all pass (12 tests: 11 existing and 1 new)

Change-Id: I18c08c1ff1a7860616b0081ede4eb19dcfa8814b