gatt/gap: Add new file for gatt/gap plugin

This patch adds a new file to implement the gatt/gap plugin based on
the new ATT API. In the future the old implementation must be removed.
gatt/gap: Add profile driver init and remove

This patch adds stubs for probe and remove gatt/gap devices.
gatt/gap: Read Device Name Characteristic

This commit adds logic to discover Device Name Characteristic from
GAP Service, read it and set the btd_device name using the response.
gatt/gap: Read Appearance Characteristic

This commit adds logic to discover Appearance Characteristic from
GAP Service, read it and set the btd_device appearance using the
response.