Do not build QQnxScreenEventThread when not needed

Change-Id: I07525ac45a610f56f2bc72731379073f4aa67f7b
Reviewed-by: Kevin Krammer <kevin.krammer@kdab.com>
Reviewed-by: Thomas McGuire <thomas.mcguire@kdab.com>
Reviewed-by: Rafael Roquetto <rafael.roquetto@kdab.com>
Move QT_CPU_FEATURES from qconfig.pri to qmodule.pri

QT_CPU_FEATURES is internal and only used by simd.prf, which is
also internal. This matches the available CPU features which are
detected using config tests and written to CONFIG in qmodule.pri.

Change-Id: I8eb35448e2954a54c228d3617f29afc0283a7db5
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>