Bluetooth: Normalize HCI_OP_READ_ENC_KEY_SIZE cmdcmplt

The HCI_OP_READ_ENC_KEY_SIZE command is converted from using the
deprecated hci_request mechanism to use hci_send_cmd, with an
accompanying hci_cc_read_enc_key_size to handle it's return response.

Signed-off-by: Brian Gix <brian.gix@intel.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>