Abi: Abi widget shows nicer info

Fix the abi widget to not show unrelated abis on the disabled
custom abi comboboxes.

Task-number: QTCREATORBUG-5370
Change-Id: I22360be781159507999c845d2278eac1ef252174
Reviewed-on: http://codereview.qt.nokia.com/1407


Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Tobias Hunger <tobias.hunger@nokia.com>