Convert Vehicle Property to integer

This make sense for easier extending Vehicle Hal interface
by OEMs and creating new versions.

Test: adb shell "su system /data/nativetest/android.hardware.vehicle@2.0-manager-unit-tests/android.hardware.vehicle@2.0-manager-unit-tests" ; ENABLE_TREBLE=true make vts BUILD_GOOGLE_VTS=true -j32 && vts-tradefed run commandAndExit vts --skip-all-system-status-check --primary-abi-only --skip-preconditions --module VehicleHidlTest -l INFO

Change-Id: I02415a1c180a6d24fded48a1583f7cb150419820
Fix: b/34894217