Bluetooth: Classic: AVRCP: Enable cover art feature

Add Kconfig `BT_AVRCP_TG_COVER_ART` to enable the target cover art
feature.

Add Kconfig `BT_AVRCP_CT_COVER_ART_GET_IMAGE_PROPERTIES` to enable
the controller cover art get image properties feature.

Add Kconfig `BT_AVRCP_CT_COVER_ART_GET_IMAGE` to enable the
controller cover art get image feature.

Add Kconfig `BT_AVRCP_CT_COVER_ART_GET_LINKED_THUMBNAIL` to enable
the controller cover art get linked thumbnail feature.

Add functions `bt_avrcp_cover_art_ct_cb_register()` and
`bt_avrcp_cover_art_tg_cb_register()` to register the callback.

Add function `bt_avrcp_cover_art_ct_l2cap_connect()` to create the
L2CAP connection for OBEX transport.

Add functions `bt_avrcp_cover_art_ct_l2cap_disconnect()` and
`bt_avrcp_cover_art_tg_l2cap_disconnect()` to disconnect the L2CAP
connection.

Add functions to send OBEX request/response, including connect,
disconnect, abort, get_image_properties, get_image, and
get_linked_thumbnail.

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

Author: lylezhu2012