unit/gatt: Rework service db definitions
unit/gatt: Rework service db definitions

Introduces a set of macros providing a simple syntax for definining a
test GATT database.

The two defined databases are reconstructed using the new format.
Some old helper methods are not used anymore and are removed.

pstglia/external-bluetooth-bluez,mapfau/bluez,silent-snowman/bluez,pkarasev3/bluez,mapfau/bluez,ComputeCycles/bluez,silent-snowman/bluez,pkarasev3/bluez,pstglia/external-bluetooth-bluez,silent-snowman/bluez,ComputeCycles/bluez,silent-snowman/bluez,mapfau/bluez,pstglia/external-bluetooth-bluez,pstglia/external-bluetooth-bluez,pkarasev3/bluez,mapfau/bluez,ComputeCycles/bluez,pkarasev3/bluez,ComputeCycles/bluez