floss: Add AG feature ESCO_S4

This is mandatory for passing HFP v1.9

Bug: 323471160
Tag: #floss
Test: mmm packages/modules/Bluetooth
Test: HFP/AG/ACS/BV-16-C on PTS v8.5.3
Test: bluetooth_AdapterAUHealth.{au_hfp_nbs_dut_as_source_test,
      au_hfp_nbs_dut_as_sink_test}.floss
Flag: EXEMPT, Floss-only changes
Change-Id: Ic9ee3bf91e73d41d4f63d40983ac452480f215de