Move PWLE notification vibration pattern to config.xml

The generic pattern coded in the notification service ignores the user
settings for vibration intensity because of the current PWLE
implementation in Android S.

Moving this to a device-specific configuration (empty by default). Each
device-specific pattern should be designed to accomodate the vibrator
frequency response curve that will be exposed by the Vibrator API.

Fix: 212366218
Test: VibratorHelperTest + manual
Change-Id: I8807ede4a13e4880f51a0075ff7c658724649265
Merged-In: I8807ede4a13e4880f51a0075ff7c658724649265