Bluetooth: HFP_HF: Support Voice recognition activation

Add configuration `CONFIG_BT_HFP_HF_VOICE_RECG` to enable Voice
recognition activation feature.

Add configuration `CONFIG_BT_HFP_HF_ENH_VOICE_RECG` to enable Enhanced
Voice Recognition Status feature.

Add configuration `CONFIG_BT_HFP_HF_VOICE_RECG_TEXT` to enable Voice
Recognition Text feature.

Add function `bt_hfp_hf_voice_recognition` to activate/deactivate the
Voice recognition activation feature.

Add function `bt_hfp_hf_ready_to_accept_audio` to indicate that the HF
is ready to accept audio.

Add a callback `voice_recognition` to notify the upper layer the
status of voice recognition activation.

Add a callback `vre_state` to notify the upper layer the state of
voice recognition engine.

Add a callback `textual_representation` to notify the upper layer the
textual representation.

Signed-off-by: Lyle Zhu <lyle.zhu@nxp.com>