Change 'HDMI' on music notification panel UI to 'External Device'

- 'HDMI' was replaced with 'External Device'
- resource 'default_audio_route_name_hdmi' was renamed to
  'default_audio_route_name_external_device'

This is a cherry-pick of changes from ag/19927045.

Bug: b/233323666
Test: Tested manually by replacing text in UMO's chip
Change-Id: I8178ab2c27b1ec1e4bbcfc244611190593d5d836
(cherry picked from commit 8b59d645)
Merged-In: I8178ab2c27b1ec1e4bbcfc244611190593d5d836