LeAudio: Add persistent storage for GMAP

For the bonded devices, service discovery is
skipped and service data needs to be restored from the persistent
storage for the GMAS client to work. The storage will not be used when
GMAP feature flag is disabled.

Bug: 383623629
Bug: 353978074
Test: atest bluetooth_le_audio_test
Flag: Exempt; Covered with unit tests
Change-Id: Ib01c38e7e6eed6103fccb70953483bb0e32abb87