iOS: don't activate non-toplevel windows

Parts of the code seems to assume that all QWindows are
top-level windows. This will be false when not using
alien, as then, each widget will be wrapped inside a
QWidgetWindow. In that case, we should not tell QPA to
activate the "window".

This bug caused focus handling (and text input) to fall
apart for e.g graphicsview when using a QGLWidget as viewport.

Change-Id: I579db7a84d718973e02e96ed535fe6e25baf4bd5
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@digia.com>