Grey out LE audio offload switcher as LE audio isn't enabled/supported

Screenshot: https://screenshot.googleplex.com/C6pRBzLh7CtNeXr

Bug: 233018305
Bug: 233005340
Test: make RunSettingsRoboTests ROBOTEST_FILTER=BluetoothLeAudioHwOffloadPreferenceControllerTest
Change-Id: I0ea498d2fa191f9b9352b37500a5d2c348b36ce0
Merged-In: I0ea498d2fa191f9b9352b37500a5d2c348b36ce0
(cherry picked from commit f71b2ea5)