Bluetooth: HFP_HF: Turn off AG's EC and NR

Add a configuration `CONFIG_BT_HFP_HF_ECNR` to enable "EC and/or NR
function" of HFP HF.

Add a function `bt_hfp_hf_turn_off_ecnr` to turn off AG's EC and NR.

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