Start eventTime timer so that the .elapsed method will work.

Start eventTime timer so that the .elapsed method will work.

QWindowSystemInterfacePrivate::eventTime.start() is never called,
resulting in all calls to
QWindowSystemInterfacePrivate::eventTime.elapsed() within
qwindowsysteminterface_qpa.cpp to return 0.  This could cause events
to be lost, such as mouse button press events from the evdevmouse
input plugin.

Change-Id: Iba9d23b51af80e8532d24ccf382e9077c06bb4be
Reviewed-by: Laszlo Agocs <laszlo.p.agocs@nokia.com>