The QtBluetooth library only builds the bluez backend when qtdbus is
enabled. Previously it was possible that dbus was disabled but the bluez
feature flag is still set. This patch prevents this gap by directly
binding the bluez feature to the dbus feature.

Change-Id: I173d51f27f5b1a78241548617f602830fec7bb14
Reviewed-by: Lars Knoll <lars.knoll@qt.io>