Floss: rework |codec_type| associated with SCO

When there were only 2 codec types, it was natural to use a boolean
variable to store which is being used. Now there are 3, we rework the
member to be associated with the type |tBTM_SCO_CODEC_TYPE|.

Bug: 269970706
Test: atest bluetooth_test_gd
Test: btclient > media log
Change-Id: I4209f172269e73f2dcb8e69eaf9e4627668d4376