directfb: fix QThread destroyed while running

Commit cf092abdfc888f19a607a43c9b4bac776b5c1f8e introduces a virtual
"void initialize()" in QPlatformIntegration class.

"void initialize()" was already implemented in QDirectFbIntegration
since commit 6534898cc69e22115cf158f71a1e0edd7f13877b allowing
initialization steps to be overridden by QDirectFbIntegrationEGL.

Therefore the QScopePointer "m_input" handling a QThread is reset twice.
The QThread firstly created is forcibly terminated. The application
displays the error message "QThread: Destroyed while thread is still
running" and sometimes crash with a SIGSEGV.

This commit rename QDirectFbIntegration::initialize() into
QDirectFbIntegration::connectToDirectFb() to fix this issue.

Task-number: QTBUG-38710
Change-Id: I3ca07c373af7c47abf08da2b45bbcf7a6cf573ad
Reviewed-by: Holger Freyther <holger+qt@freyther.de>
Reviewed-by: Laszlo Agocs <laszlo.agocs@digia.com>