Load vibration scale gain from system properties

Add support to VibrationConfig to load device configuration values from
system properties, to allow vendors to configure the device scale
factors for the different levels.

Fix: 356407380
Test: VibrationConfigTest
Flag: android.os.vibrator.haptics_scale_v2_enabled
Change-Id: Ie1f701951db33eb4ed02d7de3b6f987e6a902050